uses configMapRef instead of custom config map source

[ChrisJBurns]

We have a custom configmap source, this PR uses the corev1 configmap selector to reduce code on our side and to stay consistent with the ConfigMap ref objects.

Ref: #2352

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.47%. Comparing base (a26f8af) to head (525cdeb).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/thv-operator/api/v1alpha1/mcpregistry_types.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2621   +/-   ##
=======================================
  Coverage   55.47%   55.47%           
=======================================
  Files         312      312           
  Lines       29715    29715           
=======================================
  Hits        16485    16485           
  Misses      11790    11790           
  Partials     1440     1440           

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