Gimbal discovery using protocol bit

[hamishwillee]

This updates gimbal protocol discovery to require using the bit, as described in https://github.com/mavlink/mavlink/pull/2144.

I also took the time to

• simplify the description of mavlink vs non-mavlink gimbals. It is a lot better now.
• update the heartbeat protocol with component information basic.

Note, PX4 and ArduPilot should set the bit. FYI @rmackay9

PX4 work for this in https://github.com/PX4/PX4-Autopilot/pull/23692/files