Actions: support vehicle and autopilot shutdown and rebooting

In normal operation a user should ideally not need to access any software other than Cockpit, so it would be useful if Cockpit could safely command the vehicle to shut itself down, or reboot, and same for the autopilot.

There is [a relevant MAVLink command](https://mavlink.io/en/messages/common.html#MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN) for this, although it will currently only work for the autopilot, since BlueOS doesn't check for it. BlueOS does at least support rebooting/shutting down via its Commander API.

Start by reading the MAVLink MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN documentation and the BlueOS Commander API referenced in the issue. Determine how Cockpit should safely request shutdown and reboot for both the vehicle and autopilot; done means both targets can be commanded through Cockpit.

Written by the indexing model from the issue text.