Converge `grafana.yaml` and `grafana-frontend.yaml`

[zmerlynn]

Follow up to https://github.com/googleforgames/agones/pull/2990#discussion_r1116274926: after #2990 goes in, let's figure out how to maybe converge these manifests.

[zmerlynn]

Also leaving breadcrumbs: We need the frontend service as an authentication proxy. I'd love to get rid of it entirely, but that is blocked on: https://github.com/grafana/grafana/discussions/40844#discussioncomment-4332200 - if that issue goes away, we can remove grafana-frontend.yaml entirely.

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[markmandel]

Maybe a good use for kustomize ? to only have a single yaml reference, but can change the datasources.url as needed?

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