[UGV] Add a new navigation state for stopping the vehicle without disarming

[chfriedrich98]

Describe problem solved by the proposed feature

There is currently no navigation state to simply stop a vehicle (send disarm values to motors) without disarming the vehicle. This would be useful for ground vehicles as both a failsafe navigation state and as a replacement for Land and Descend.

Describe your preferred solution

Add new navigation state Stop which sends disarm values to all actuators without disarming. This navigation state should have no requirements on estimates of position, velocity, etc.

Describe possible alternatives

Additional context

No response