Add service mesh `Policies` for all Coordinator relations

### Enhancement Proposal

To enable adding Coordinated-Workers a service mesh, we need to implement any required service mesh `Policies` to allow inbound communication to Coordinator. This includes:

* anything related via the [metrics](https://github.com/canonical/cos-coordinated-workers/blob/a008e0f43f5ed3e56e6df94427bb75dc8e222f7d/src/coordinated_workers/coordinator.py#L169) endpoint
* anything else that needs these

To be decided is whether a Policy should be added for the Worker->Coordinator traffic, or whether that should just use a custom Authorization Policy like other intra-solution traffic

Start with the metrics endpoint referenced in src/coordinated_workers/coordinator.py and map every Coordinator relation that requires inbound service-mesh access. Review the existing intra-solution authorization approach, then resolve whether Worker-to-Coordinator traffic needs a Policy or a custom Authorization Policy. Done means all required Policies are identified and implemented for the Coordinator relations.

Written by the indexing model from the issue text.