related to https://issues.redhat.com/browse/ACM-27104

Issue : with ACM 2.14, if the hub is created and not upgraded from older versions, the ImportOnly import strategy is set by default, meaning that a managed cluster is not reimported if already known by the hub

This is to support uncontrolled DR, when the primary hub goes down unexpectedly then later on comes back and tries to reconnect the managed clusters which were already moved to another hub.

When ImportOnly is set, a simulation failover will ( move back to the primary hub after restore ) will not reimport the clusters , and this is an issue

To address this, before restore starts, we should set the `immediate-import` annotation on ManagedClusters with an empty value

Regarding the `immediate-import` annotation: once it is added to a cluster, there is no need to remove it. Only an annotation with an empty value can trigger the auto-import process. Once the auto-import completes, the value is set to `Completed`. An annotation with a non-empty value will not trigger another auto-import attempt. This behavior is also documented in the ACM-DDR-040. You can refer to it for further details.

import.open-cluster-management.io/immediate-import: ''