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 86.86%. Comparing base (94a2edc) to head (c2286c3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3735      +/-   ##
==========================================
- Coverage   86.89%   86.86%   -0.04%     
==========================================
  Files         128      128              
  Lines       16187    16187              
  Branches       62       62              
==========================================
- Hits        14066    14061       -5     
- Misses       1949     1953       +4     
- Partials      172      173       +1     

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[sjberman]

I feel like a lot of these separate test functions could just be combined into one, to reduce duplication. They are ultimately formatted and testing very similar things. For example, 3 different test functions that are testing the TargetRef field. Could be one large list of structs in a single test IMO.