Report dock status

[andchiind]

Describe the new feature you would like to see
ISAR should be aware of whether or not it is docked/home, and this should be reported using MQTT. This could either be implemented as a state (which would basically act the same as "idle"), or it could be an independent telemetry. One solution is to send the MQTT message in a transition to idle, so if a return home mission completes then we send the message as we transition to idle, and if we transition away from idle, or we transition to idle without docking, then we report that we are outside the dock/home.

Describe the solution you'd like
I personally think this should not report whether or not it is charging, as this is better done as a part of the battery telemetry, but it should just report that its location is "docked" or "home".

How will this feature affect the current Threat Model?
Leave blank for maintainers to fill out if you are uncertain about this.