[Investigation] How to make Grafana Panels compatible with Snapshots

For  PMM-3831 and related issues, we need to understand and document how to make our panels work (show the panel's data) when it's sent (i.e. persisted or saved for future reference) to a snapshot server (example: https://snapshots-g635.percona.com/) and not saved as a local snapshot (local to a PMM server).

Our internal term for this problem is: shapshot-compatible panels.

For more insight on how it used to work in older Grafana versions please refer to https://grafana.com/docs/grafana/latest/developers/plugins/legacy/snapshot-mode/