fix: de-duplication of custom resource metrics

[bartlettc22]

What this PR does / why we need it:
Fixes an issue that causes custom resource metrics to duplicate every time a CR resource that KSM is watching changed. The duplication was happening because the informer events (add/delete) triggered a subsequent call to WithEnabledResources in store.Builder. This would append, but not de-duplicate the CR resources to the enabledResources list. This, in turn, would cause the custom resources to be be added multiple times when the store was built.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
Does not change cardinality

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #2446

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: bartlettc22 / name: Chris Bartlett (24c2194, de58db2)

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[dgrisonnet]

/assign @rexagod
/triage accepted

[rexagod]

Requested a minor change below. Thank you for the much needed patch!

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[bartlettc22]

Requested a minor change below. Thank you for the much needed patch!

@rexagod updated - thanks for the suggestion!