Add CEL function to parse YAML

[chetan-rns]

Changes

This PR will add a CEL function named parseYAML that can parse a YAML string into a map of strings to dynamic values

Syntax: .parseYAML() -> map<string, dyn>

Fixes: #622

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• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
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Release Notes

 'parseYAML' is a CEL function that can parse YAML body in string to a map.

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/interceptors/cel/triggers.go	87.2%	88.3%	1.1

[wlynch]

We should also test/document behavior for nested types, since this came up with JSON support as well.

/cc @bigkevmcd

[wlynch]

But otherwise LGTM! Thanks for the contribution! :)

[bigkevmcd]

We should also test/document behavior for nested types, since this came up with JSON support as well.

Both the JSON parsing and YAML parsing end up going through the same marshaling into the output JSON.

Any differences should (theoretically) be down to the parsers themselves (ints/floats/strings/maps etc).

[bigkevmcd]

/lgtm

[tekton-robot]

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

File	Old Coverage	New Coverage	Delta
pkg/interceptors/cel/triggers.go	87.2%	88.3%	1.1

[bigkevmcd]

/lgtm

[bigkevmcd]

/approved

[dibyom]

Thanks @chetan-rns !
/approve

[tekton-robot]

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