✨ Add Service Account requirement to ClusterExtension

[makon57]

Description

This PR solves Issue #971 - Add new required field to ClusterExtension spec for users to reference a ServiceAccount

• Created new required 'Service Account' field in ClusterExtensionSpec
• Added Service Account to unit tests
• Added Service Account to e2e test

Reviewer Checklist

• API Go Documentation
• Tests: Unit Tests (and E2E Tests, if appropriate)
• Comprehensive Commit Messages
• Links to related GitHub Issue(s)

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[codecov]

Codecov Report

Attention: Patch coverage is 11.11111% with 8 lines in your changes missing coverage. Please review.

Project coverage is 77.57%. Comparing base (235e3d4) to head (c6560b4).
Report is 1 commits behind head on main.

Files	Patch %	Lines
api/v1alpha1/zz_generated.deepcopy.go	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1011      +/-   ##
==========================================
- Coverage   78.05%   77.57%   -0.48%     
==========================================
  Files          18       18              
  Lines        1253     1262       +9     
==========================================
+ Hits          978      979       +1     
- Misses        193      201       +8     
  Partials       82       82              

Flag	Coverage Δ
e2e	56.31% <11.11%> (-0.35%)	⬇️
unit	53.09% <0.00%> (-0.39%)	⬇️

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