Logging start / restart by Mavlink command

## Feature request

**Is your feature request related to a problem? Please describe.**
1) Disarmed logging can only started by setting up LOG_DISARMED to 1. But if set to 1, it logs always until LOG_DISARMED is set to 0 again.
2) Endurance tests often creates huge logs in which it is difficult to find and review a specific period or event

**Describe the solution you'd like**
Add a possibility of starting / restarting logging by Mavlink command, through MissionPlanner, or other QGC apps.

Operation :
1) If the vehicle is disarmed, this command triggers a log recording start.
2) If logging is already running, this command ends up the actual log and starts another one. This can be useful to separate specific sections of a test flight into different logs.
Especially when raw IMU logging is enabled, which increases log sizes by a lot.

**Describe alternatives you've considered**
I didn't find another way of restart logging in the air.

**Platform**
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Submarine

**Additional context**
Possible MissionPlanner command in the Action menu:

No files, tests, or entry points are named. Begin by locating the existing LOG_DISARMED logging path and MAVLink command handling, then determine how command-triggered log rotation should work across all vehicle platforms. Done means the command starts logging when disarmed and ends the current log before starting a new one when logging is active.

Written by the indexing model from the issue text.