[Request] Multi cluster support for kubernetes discovery

### Describe the feature

Having several kubernetes clusters in the same service mesh, it would be good for Cryostat being able to discover targets in other clusters

### Anything other information?

_No response_

The issue names no files, tests, or entry points. Start by mapping the existing Kubernetes discovery flow and how targets are associated with a service mesh, then determine the requirements for discovering targets across multiple clusters. Done means multi-cluster targets are discoverable without breaking existing single-cluster behavior.

Written by the indexing model from the issue text.