grafana-app release v2.40.0

Brand Grafana with the Giant Swarm logo mark and favicon, by mounting the assets in helm/grafana/branding over the ones the Grafana image ships. Set grafana.extraConfigmapMounts to [] to get Grafana’s own branding back.
Add make branding-verify (run by the verify-branding CI job) and make branding-update, which keep the hashed logo path in sync with the Grafana image and generate the pod annotation that rolls the deployment when a branding asset changes.