Support FedCluster

### 🚀 Feature Description and Motivation

I'm evaluating to introduce aibrix into our production clusters. But our clusters are "FedClusters". I wonder if aibrix is able to deploy in fedclusters. Because our inference-instances are deployed across difference clusters.

### Use Case

Given a fedclsuter kube-config, and everything keeps same as in-cluster scheduling.

I'm not familiar with fed-cluster. I guess my request could be fulfilled as long as the config is fed-cluster level, isn't it?

### Proposed Solution

_No response_

The issue names no files, tests, or entry points. Start by clarifying what FedCluster support and kube-config behavior are expected to cover; the description provides no acceptance criteria or definition of done, so the implementation scope cannot be determined from the issue alone.

Written by the indexing model from the issue text.