bug: TypeError: k8 service discovery fail to load config

Describe the bug

I was in the process of unit testing the K8sPodIPServiceDiscovery class

I wanted to mock the config.load_incluster_config() so that it returns a config.ConfigException

Here is the error I got from python:

# Init kubernetes watcher
        try:
            config.load_incluster_config()
>       except config.ConfigException:
E       TypeError: catching classes that do not inherit from BaseException is not allowed

To Reproduce

When initializing K8sPodIPServiceDiscovery, mock the config.load_incluster_config() so that it returns a config.ConfigException

Expected behavior

It should not raise a TypeError

Additional context

The faulty code is:

        # Init kubernetes watcher
        try:
            config.load_incluster_config()
        except config.ConfigException:
            config.load_kube_config()

In https://github.com/vllm-project/production-stack/blob/main/src/vllm_router/service_discovery.py#L375 and https://github.com/vllm-project/production-stack/blob/main/src/vllm_router/service_discovery.py#L794

By the way, I see quite a bit of overlap between K8sServiceNameServiceDiscovery and K8sPodIPServiceDiscovery, it might be worth refactoring 😄

Start in src/vllm_router/service_discovery.py at the two locations linked in the issue and inspect how K8sPodIPServiceDiscovery initializes its watcher. Reproduce the unit-test scenario around config.load_incluster_config() and compare it with the expected fallback behavior. Done means initialization no longer raises the reported TypeError and the relevant test passes.