dev: Grafana generated dashboards not loading on startup

Created by: slimsag

when the server first starts up it will use the dashboards baked into the base container (it was previously built). Only when you save a file will it regenerate and actually pick up the changes.

The generated dashboards are not mounted properly into the container (the deprecated jsonnet ones are, though): https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/dev/grafana.sh#L23-38