transition from endpoints to endpointslices

[mpetitjean22]

After upgrading our clusters to k8s 1.33, we started to see the following warning from jupyterhub (specifically user-scheduler component):

Warning: v1 Endpoints is deprecated in v1.33+; use discovery.k8s.io/v1 EndpointSlice

Kubernetes provides some more details here about why + what the fix would look like.