Preserve external controller state during reconciliation

[ciarams87]

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Proposed changes

Problem: NGINX Gateway Fabric's provisioner removes all annotations during service reconciliation that aren't explicitly managed by NGF. This causes conflicts with external controllers that need to add operational annotations.

Solution: Implemented a preservation pattern for both service annotations by merging Service annotations instead of overwriting

Testing: Unit testing, manual testing in progress

Please focus on (optional): If you any specific areas where you would like reviewers to focus their attention or provide specific feedback, add them here.

Closes #4012 Closes #4175

Checklist

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• [ ] 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

Release notes

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Preserve external controller annotations