Adds a new scheduled task (default every 5 mins but configurable) to make requests to initiate Grafana instances to send sync data to OnCall
Backend plugin sync endpoint can also be used to manually send sync data.
Backend plugin sync endpoint adds lock so only 1 can sync at a time, currently returns 400 if already in use. Callers are engine and manual users so this should be ok, engine will just log it.
Removed routes from plugin.json (I don't think we need these anymore)
Needed to add plugins.app:access permission to engine can call plugin.