[Feature Request] [occm] Controller to clean-up OCCM orphaned openstack ressources

/kind feature

**What happened**:

If we provision a cluster with OCCM controlled resources, then delete it directly, OCCM can't and will never remove openstack resources.
This is because the cluster and the controller are removed before any garbage collection and proper cascading deletion can happen.

**What you expected to happen**:

This is not something we can solve in OCCM itself as it is getting removed.
We need another controller running outside of the said provisioned cluster to manage and detect orphaned resources.

**How to reproduce it**:

- Provision a cluster
- Deploy OCCM on it
- Create some OCCM CRs (loadbalancer?, network?)
- OCCM provision thoses resources in Openstack
- Delete the cluster directly
- The openstack resources are now orphaned

**Anything else we need to know?**:

This is a common use case when using Cluster API openstack provider and OCCM.
I think such feature would help keeping openstack free from orphaned resources and the need to clean that up manually.

The issue names no files, tests, or entry points. Start with the listed cluster/OCCM/OpenStack reproduction, then define the external controller’s orphan-detection and cleanup scope; done means resources left after direct cluster deletion are identified and cleaned without the deleted controller.

Written by the indexing model from the issue text.