Enables a Grafana service pointing to whitby's local Prometheus
instance, accessible at status.tvl.su.
I've no idea how to configure Grafana and if it's possible to link it
to CAS, but we'll see about that later.
Notes:
* the explicit fixpoint for whitby config has been removed as we
have the `config` parameter available now
* backups are enabled for the Grafana storage location
Change-Id: If5ffe0c1a3378d1c88529129487c643642705fd2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2948
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>