Improve exception handling for listing Kubernetes resources

[josefhandl]

When the Kubernetes API fails to list Kubernetes resources in the reflector (for example too strict permissions), no relevant error message appears in the logs, and the program fails. I'm adding a check to see if the call is successful. If not, an error with the API is printed, and an exception is thrown.

This is what the previous logs look like (enable_user_namespaces = True):

[I 2024-05-02 13:20:03.726 JupyterHub spawner:188] Using user namespace: user-jhu
[E 2024-05-02 13:20:03.739 JupyterHub reflector:412] Initial list of pods failed
    Traceback (most recent call last):
      File "/opt/kubespawner/kubespawner/reflector.py", line 410, in start
        await self._list_and_update()
      File "/opt/kubespawner/kubespawner/reflector.py", line 249, in _list_and_update
        for p in initial_resources["items"]
    KeyError: 'items'

[E 2024-05-02 13:20:03.739 JupyterHub spawner:2411] Reflector with key ('pods', None) failed to start.
    Traceback (most recent call last):
      File "/opt/kubespawner/kubespawner/spawner.py", line 2409, in catch_reflector_start
        await func
      File "/opt/kubespawner/kubespawner/reflector.py", line 410, in start
        await self._list_and_update()
      File "/opt/kubespawner/kubespawner/reflector.py", line 249, in _list_and_update
        for p in initial_resources["items"]
    KeyError: 'items'

...and this now:

[I 2024-05-02 13:20:26.046 JupyterHub spawner:188] Using user namespace: user-jhu
[E 2024-05-02 13:20:26.059 JupyterHub reflector:237] Error when calling Kubernetes API. Status: 403 Forbidden. Message: pods is forbidden: User "system:serviceaccount:default:jupyterhub-spawner-sa" cannot list resource "pods" in API group "" in the namespace "user-jhu"
[E 2024-05-02 13:20:26.059 JupyterHub reflector:412] Initial list of pods failed
    Traceback (most recent call last):
      File "/opt/kubespawner/kubespawner/reflector.py", line 410, in start
        await self._list_and_update()
      File "/opt/kubespawner/kubespawner/reflector.py", line 240, in _list_and_update
        raise client.ApiException(
    kubernetes_asyncio.client.exceptions.ApiException: (403)
    Reason: Forbidden

[E 2024-05-02 13:20:26.059 JupyterHub spawner:2411] Reflector with key ('pods', None) failed to start.
    Traceback (most recent call last):
      File "/opt/kubespawner/kubespawner/spawner.py", line 2409, in catch_reflector_start
        await func
      File "/opt/kubespawner/kubespawner/reflector.py", line 410, in start
        await self._list_and_update()
      File "/opt/kubespawner/kubespawner/reflector.py", line 240, in _list_and_update
        raise client.ApiException(
    kubernetes_asyncio.client.exceptions.ApiException: (403)
    Reason: Forbidden

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[consideRatio]

@yuvipanda I tried catching up with differences of log.error and log.exception, but I've not come to a conclusion if 0f2555d was what you wanted - could you review this again?

[yuvipanda]

I think either works, and given that the ultimate goal is to figure out better error handling, I'm just going to merge this.

Thanks for your patience @josefhandl and thanks for the ping, @consideRatio