util/sets package provides a better interface to handle sets

Fixed #1765

Summary by cubic

Replaced all map[string]struct{} “sets” with k8s.io/apimachinery/pkg/util/sets across the operator. This standardizes set ops (Has/Insert), reduces boilerplate, and keeps behavior the same.

• Refactors
  • Switched disabled-controller tracking, flag parsing, and all “keep” lists to sets.Set[string] (services, scrapes, PDBs, HPAs, VPAs, STSs, Deployments).
  • Updated ChildCleaner and RemoveOrphaned* function signatures/tests to use sets; simplified delete checks to Has.
  • Used sets in reconcile mergeMaps (deleted keys) and StatefulSet validation (volume names).
  • Simplified IsControllerDisabled and manager disabled-controller checks with sets.

^{Written for commit 6288ab1. Summary will update on new commits.}