Fix/OIDC - relaxed OIDC scope validation

[jjngx]

Proposed changes

This PR introduces following changes:

• relaxed OIDC scope validation - only scope openid is required, users can use their own custom scopes
• added validation rules for users' defined scope tokens to comply with RFC6749 (except char "+" \x2b used internally to separate tokens in scopes)
• added tests and improved test coverage
• cleaned up tests for policies validators, separated valid and invalid inputs for validators (no business rules change!)

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• [] I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[codecov]

Codecov Report

Merging #3863 (0a7c9bc) into main (adba092) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head 0a7c9bc differs from pull request most recent head 22e2007. Consider uploading reports for the commit 22e2007 to get more accurate results

@@            Coverage Diff             @@
##             main    #3863      +/-   ##
==========================================
- Coverage   51.95%   51.94%   -0.02%     
==========================================
  Files          59       59              
  Lines       16759    16746      -13     
==========================================
- Hits         8707     8698       -9     
+ Misses       7756     7748       -8     
- Partials      296      300       +4     

Impacted Files	Coverage Δ
pkg/apis/configuration/validation/common.go	100.00% <100.00%> (ø)
pkg/apis/configuration/validation/policy.go	92.91% <100.00%> (+1.28%)	⬆️

... and 2 files with indirect coverage changes

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[lucacome]

Looks like there are unrelated changes, but I think they go away after #3818 is merged?

[shaun-nx]

🚀