Kube-controller-manager having frequent errors as "GarbageCollectorDegraded: alerts firing: GarbageCollectorSyncFailed" due to unwanted/stale ACM resources in the cluster

Issue

• 4.11.z cluster upgrade finishes but kube-controller-manager CO is degraded with the below error:

- {message: 'GarbageCollectorDegraded:
      alerts firing: GarbageCollectorSyncFailed', reason: GarbageCollector_Error,
    status: 'True', type: Degraded}

• If the Cluster has stale RHACM resources, wherein RHACM was not properly removed as per following the relevant documentation and article.

• Missing webhook error when trying to list ManagedClusterSet custom resource.

Error from server: conversion webhook for cluster.open-cluster-management.io/v1beta1, Kind=ManagedClusterSet failed: Post "https://cluster-manager-registration-webhook.open-cluster-management-hub.svc:9443/convert?timeout=30s": service "cluster-manager-registration-webhook" not found