Create workflow for providing provisioned dashboards

[chrisys]

Allow users to supplement the auto-generated dashboards with their own pre-created ones. In the case of Grafana this can be implemented by providing .json dashboard files within the provisioning/dashboards folder.

[alanb128]

@chrisys I think this is already in place? I tried this with balenaSense and Phil did so with the Speedtest. After a discussion with Phil, what we would like to do is move the provisioning folder to a persistent volume so you don't have to include pre-created dashboards in the build like you do now. It looks like this can be accomplished by overriding user settings in grafana.