Add helmfile deployment for Grafana

Part of https://gitlab.com/gitlab-com/gl-infra/reliability/-/issues/16910

This will deploy Grafana using the official Helm chart into a new namespace grafana in the pre and ops clusters, to replace the Grafana deployment in tanka-deployments (https://gitlab.com/gitlab-com/gl-infra/k8s-workloads/tanka-deployments/-/tree/master/environments/grafana).

Upstream PRs

• [grafana] Allow to configure HPA scaling behavior and add autoscaling for grafana-image-renderer
• [grafana] Add a ServiceMonitor for grafana-image-renderer

TODO

• PDB for grafana-image-renderer