🐛 Fix OpenStackServer reconciliation stuck when cluster is unpaused

[bnallapeta]

What this PR does / why we need it:
When a cluster is paused (e.g., during a pivot operation), OpenStackServer resources stop reconciling. However, when the cluster is unpaused, they don't resume because the controller doesn't watch for cluster pause/unpause events.

This PR adds a watch on Cluster resources so OpenStackServers are re-queued when their parent cluster transitions from paused to unpaused state.

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 #2824

TODOs:

• squashed commits
• if necessary:
  • includes documentation
  • adds unit tests

/hold

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[EmilienM]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: EmilienM

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[bnallapeta]

/ok-to-test

[lentzi90]

Don't we need to clean up if it is deleting? I am thinking that there could be a situation where the user paused the cluster, then deleted (forgetting to unpause first), then unpause.

[bnallapeta]

hmm, to address this edge case, here's what I did:
I've moved the pause check after the deletion timestamp check (similar to OpenStackCluster controller). Now the reconciliation flow is:

1. Check if server is being deleted -> proceed with deletion (regardless of pause state)
2. If not deleted, check if cluster is paused -> skip reconciliation
3. Otherwise, proceed normally

This ensures deletion always proceeds even if the cluster was paused when deletion started, then later unpaused.

[bnallapeta]

@lentzi90 ptal ^^

[lentzi90]

I am a bit worried that this will break clusterctl move. We will probably need to handle all these cases:

1. Cluster paused and has deletion timestamp: do nothing <- This is now broken I think (we delete even when paused)
2. Cluster unpaused and has deletion timestamp: reconcileDelete <- This was missing in first version I think
3. Cluster paused and no deletion timestamp: do nothing ✔️
4. Cluster unpaused and no deletion timestamp: reconcileNormal ✔️

The full test is testing clusterctl move, so let's check
/test pull-cluster-api-provider-openstack-e2e-full-test

[k8s-ci-robot]

@bnallapeta: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cluster-api-provider-openstack-e2e-full-test	828af4f	link	false	/test pull-cluster-api-provider-openstack-e2e-full-test

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