feat(Grafana): K8s serviceaccount token as authorization .spec.client.useKubeAuth

[Baarsgaard]

Use the k8s ServiceAccount token projected in at /var/run/secrets/kubernetes.io/serviceaccount/token as authentication to Grafana instances.

Users can configure [auth.jwt] to accept K8s ServiceAccounts and assign them roles depending on the name, namespace, etc in the JWT token and entirely disable the default Grafana admin account.

TODO

• Docs/Examples: https://gist.github.com/Baarsgaard/38217259c5e2f72af28ae8b8792fb54e
  Maybe as a separate PR so it does not show in the docs until released with v5.20.0
• Simplify Grafana configuration by merging: Auth: Support JWT configs tls_client_ca and jwk_set_bearer_token_file grafana#109095

Questions:

• Should the operator support a default config for JWT auth which is used? The variance in what people want might be a bit high and instead just document the options.
• Name of the client option? useKubeAuth and useJWTAuth are both a bit vague
• Should this be merged after Grafana v12.2.0 is released and configured as the new default version?
  Would help a lot for usability as the the full setup can be handled in the Grafana CR