initial external data integration for validation

[sozercan]

Signed-off-by: Sertac Ozercan sozercan@gmail.com

What this PR does / why we need it:
As discussed this is the initial PR for external data for validation only. After this is merged, I'll rebase #1506 for mutation.

Depends on open-policy-agent/frameworks#134

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):
Fixes #

Special notes for your reviewer:

[codecov-commenter]

Codecov Report

Merging #1573 (e507129) into master (86da9a8) will increase coverage by 0.11%.
The diff coverage is 61.86%.

@@            Coverage Diff             @@
##           master    #1573      +/-   ##
==========================================
+ Coverage   54.25%   54.37%   +0.11%     
==========================================
  Files          93       94       +1     
  Lines        8082     8193     +111     
==========================================
+ Hits         4385     4455      +70     
- Misses       3356     3391      +35     
- Partials      341      347       +6     

Flag	Coverage Δ
unittests	54.37% <61.86%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
apis/status/v1beta1/zz_generated.deepcopy.go	0.00% <ø> (ø)
pkg/controller/config/config_controller.go	65.04% <0.00%> (-0.29%)	⬇️
...onstrainttemplate/constrainttemplate_controller.go	59.04% <0.00%> (-0.15%)	⬇️
pkg/mutation/match/zz_generated.deepcopy.go	0.00% <ø> (ø)
...controller/externaldata/externaldata_controller.go	57.37% <57.37%> (ø)
pkg/readiness/ready_tracker.go	69.39% <67.92%> (-0.44%)	⬇️
pkg/readiness/setup.go	53.84% <100.00%> (ø)
pkg/watch/replay.go	81.25% <0.00%> (+2.27%)	⬆️

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[maxsmythe]

The overall shape of this LGTM, but haven't had time to give it a close read

[maxsmythe]

LGTM after TODO and minor comments addressed.

[ritazh]

LGTM

pending framework vendoring test failure