[SPIKE] Add support for multicluster-runtime

[maximiliantech]

Description

Adopt multicluster-runtime to support the use case of reconciling metric APIs from multiple k8s API servers.

This is needed to support as-a-service concepts (e.g. Service Provider concept at OpenMCP) this operator should be multi-cluster-aware.

Tasks

• Research how other open source tools already use multicluster-runtime
• Switch from controller-runtime to multicluster-runtime

Acceptance Criteria

• ...
• metrics-operator should behave the same as with controller-runtime
• Recommendation or documentation whether support of this runtime could be valuable in other areas also
• Successful demonstration in review meeting

[maximiliantech]

Let's bring this directly to the next Refinement. I would categorise this issue as a spike, since the work here would be very experimental.