feat: add v2alpha3 format

[aaron-prindle]

Fixes #1026

This PR adds a v2alpha3 format which uses Tekton v1 object(s) in it's Payload information. For backwards compatibility, v2alpha2 and below versions use Tekton v1beta1 object(s) in their Payload information so this is first/only format currently that uses Tekton v1 objects E2E (doesn't convert to v1beta1 in format/*)

This PR is the second part of the in the v1beta1 -> v1 tektoncd/chains work split that was identified here:
#1016 (review)

Once this is in, the workstream there should be complete

[tekton-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[aaron-prindle]

Thanks @wlynch for the reviews on #1016! 🎊 This PR is the second part of the in the v1beta1 -> v1 tektoncd/chains work split that was identified here:
#1016 (review)

Once this is in, the workstream there should be complete

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/internal_parameters/internal_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[vdemeester]

❤️

[chitrangpatel]

/approve

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: chitrangpatel, vdemeester

The full list of commands accepted by this bot can be found here.

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• OWNERS [chitrangpatel]

Approvers can indicate their approval by writing /approve in a comment
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[wlynch]

Overall looks good!

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/externalparameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/internal_parameters/internal_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[aaron-prindle]

I believe all review feedback has been addressed now:

• Updated docs/config.md to include slsa/v2alpha2 & slsa/v2alpha3 and NOTESs to explain their differences + recommended format version for new users.
• Refactored v2alpha2 and v2alpha3 external_parameters/ code to de-dupe code (namely function buildConfigSource').
• Additionally de-duped internal_parameters/, resolved_dependecies/, and build_type (all dupe locations)

lmk if there is any additional feedback or items to address. Thanks!

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/externalparameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/internal_parameters/internal_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/external_parameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/internal/internal_parameters/internal_parameters.go	Do not exist	0.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/external_parameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/internal/internal_parameters/internal_parameters.go	Do not exist	0.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/external_parameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/internal/internal_parameters/internal_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	87.5%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-chains-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/chains/formats/slsa/internal/external_parameters/external_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/internal/internal_parameters/internal_parameters.go	Do not exist	100.0%
pkg/chains/formats/slsa/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	60.0%
pkg/chains/formats/slsa/v2alpha2/internal/external_parameters/external_parameters.go	87.5%	80.0%	-7.5
pkg/chains/formats/slsa/v2alpha2/internal/resolved_dependencies/resolved_dependencies.go	86.4%	83.5%	-2.8
pkg/chains/formats/slsa/v2alpha3/internal/external_parameters/external_parameters.go	Do not exist	80.0%
pkg/chains/formats/slsa/v2alpha3/internal/pipelinerun/pipelinerun.go	Do not exist	83.8%
pkg/chains/formats/slsa/v2alpha3/internal/resolved_dependencies/resolved_dependencies.go	Do not exist	85.3%
pkg/chains/formats/slsa/v2alpha3/internal/taskrun/taskrun.go	Do not exist	86.5%
pkg/chains/formats/slsa/v2alpha3/slsav2.go	Do not exist	87.5%

[wlynch]

I think there's probably more refactoring we can do to leverage TektonObject to reduce duplication across v2alpha2 and v2alpha3, but I won't let this block the PR. LGTM!

/lgtm