⚠ Implement API changes according to RFC spec

[jsm84]

resolves#1088

Summary:

• v1 API now uses a SourceConfig discriminated union which will allow modularity for future install sources (bundles, charts, etc).
• SourceConfig uses CEL validation to ensure only valid field names & values are utilized (sourceType: Catalog ensures that the catalog field is also set in SourceConfig).
• Added new clusterextension_admission unit test for SourceConfig objects. The test covers both valid and invalid cases.
• Fixed clusterextension_controller test where an unset ClusterExtension spec caused a null pointer deref.
• Moved ClusterSelector from ClusterExtension.Spec to ClusterExtension.Source.Catalog
  and renamed to Selector.
• Updated GoDocs to reflect the new API spec and included post-review changes
• Fixed all definitions of kind: ClusterExtension in docs and scripts
  to reflect the API changes.

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[everettraven]

Thanks for this PR @jsm84 !

Requesting changes on my current comments. I'll be out tomorrow, so I'll circle around for further review on Monday.

[codecov]

Codecov Report

Attention: Patch coverage is 57.14286% with 12 lines in your changes missing coverage. Please review.

Project coverage is 77.18%. Comparing base (bf7f766) to head (8e55961).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
api/v1alpha1/zz_generated.deepcopy.go	45.45%	12 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@## main #1166 +/- ##
==========================================
- Coverage 77.55% 77.18% -0.38% 
==========================================
Files 35 35 Lines 1916 1937 +21 ==========================================
+ Hits 1486 1495 +9 - Misses 296 308 +12 
Partials 134 134 

Flag	Coverage Δ
e2e	58.59% <53.57%> (-0.18%)	⬇️
unit	54.67% <21.42%> (-0.60%)	⬇️

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[everettraven]

Just finished combing through the rest of the PR and I don't have any additional comments

[everettraven]

Some more comments on the comments. Overall I think they are good.

[everettraven]

Changes looks good to me, thanks for the contribution @jsm84 !

I finished my review on mobile and it doesn't look like I can kick CI via the GH mobile app. I'll kick it first thing tomorrow morning and try to get this merged.

[everettraven]

Closing and re-opening to try and reset the netlify checks that seem to be stuck