Grafana was still pointing at the (now non-existent) CAS setup. This
changes the endpoints to use Keycloak instead and updates the client
secret.
Change-Id: Ib25d38330aba2ef6d894e8c33d86852c884ab5be
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4706
Tested-by: BuildkiteCI
Autosubmit: tazjin <mail@tazj.in>
Reviewed-by: grfn <grfn@gws.fyi>