Add CEL validation tests for ObservabilityPolicy CRD

[shaun-nx]

Proposed changes

This change adds test for the CEL validation for the ObservabilityPolicy CR

Closes #3670

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.95%. Comparing base (003eccc) to head (ddd0271).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3735      +/-   ##
==========================================
- Coverage   86.96%   86.95%   -0.02%     
==========================================
  Files         128      128              
  Lines       15986    15986              
  Branches       62       62              
==========================================
- Hits        13903    13901       -2     
- Misses       1917     1918       +1     
- Partials      166      167       +1     

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