fix: Allow creating proj tokens in namespaces (#15333)

[iandelahorne]

Adds an optional group to the regex validating the policy object, allowing for creating API tokens for projects where a policy is targeting my-project/my-namespace/app-prefix*

Fixes #15333

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Toolchain Guide
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
• I have signed off all my commits as required by DCO
• I have written unit and/or e2e tests for my change. PRs without these are unlikely to be merged.
• My build is green (troubleshooting builds).
• I have added a brief description of why this PR is necessary and/or what this PR solves.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (92ce5a4) 49.92% compared to head (8b313ff) 49.93%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #15334   +/-   ##
=======================================
  Coverage   49.92%   49.93%           
=======================================
  Files         263      263           
  Lines       45223    45223           
=======================================
+ Hits        22578    22581    +3     
+ Misses      20427    20425    -2     
+ Partials     2218     2217    -1     

Files Changed	Coverage Δ
pkg/apis/application/v1alpha1/types.go	58.84% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[jsoref]

It feels like this needs:

1. Tests
2. Documentation
3. Release notes