BlueOS should allow having the MAVLink router working without a vehicle running

Today, if the autopilot is disconnected, the router will be killed every X seconds to try reconnecting the autopilot.
[There are cases](https://discuss.bluerobotics.com/t/how-do-i-use-mavlink-endpoints-to-get-gamepad-data/16671/16) where the user does not have an Ardupilot/PX4 autopilot running, but wants to use MAVLink anyway (for sensor communication, controls, etc), and for that there could be an option for allowing it (disabling the auto-killing of the router).

Start by locating the MAVLink router's autopilot reconnect and auto-kill logic, then read the linked discussion for the sensor and gamepad use case. Done means an option allows the router to remain running when no ArduPilot or PX4 vehicle is connected, while the existing reconnect behavior remains available.

Written by the indexing model from the issue text.