refactor EndpointSlice controller

[pdabelf5]

Proposed changes

This change moves the Endpoint Slice controller code to it's own file to help reduce the complexity of controller.go.

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

Attention: Patch coverage is 0% with 85 lines in your changes missing coverage. Please review.

Project coverage is 53.01%. Comparing base (a079805) to head (67c4a9f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/k8s/endpoint_slice.go	0.00%	85 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6323      +/-   ##
==========================================
- Coverage   53.05%   53.01%   -0.04%     
==========================================
  Files          77       79       +2     
  Lines       15921    15921              
==========================================
- Hits         8447     8441       -6     
- Misses       7069     7073       +4     
- Partials      405      407       +2     

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