Cockpit: document available protocols (MAVLink, Cockpit Actions, etc)

[ES-Alexander]

We currently mention that joystick buttons can be assigned to Actions, but don't specify which actions are available or how they work / will be customisable in future.

[ES-Alexander]

Current actions: https://github.com/bluerobotics/cockpit/blob/master/src/libs/joystick/protocols.ts#L94-L99

[ES-Alexander]

Wait for @rafaellehmkuhl, because the system is currently undergoing some changes.

[ES-Alexander]

• Cockpit Actions (see list above)
  • Interface and widget control
  • Currently a couple of normal MAVLink messages are sent via this too (to support non-ROV vehicles)
• MAVLink MANUAL_CONTROL button functions (defined by the vehicle parameters)
  • Button number limits
  • Sends MANUAL_CONTROL messages at 25Hz, currently not configurable
  • Decision process for mapping to minimise intrusiveness
    1. First tries to use already mapped functions
       • e.g. if there's already a BTNn_FUNCTION configured to Arm, then a Cockpit Arm button will map to that function bit
    2. Then overwrites Disabled BTNn_FUNCTIONs
    3. Then tries to overwrite mapped functions that Cockpit isn't using
    4. If you try to change a Cockpit function to a MAVLink function when there are no buttons left it will give a warning about running out of buttons
    • All mapping can be done with the vehicle disconnected - it will automatically remap once the vehicle connects
      • This may result in warnings if you've assigned too many button functions
• Other
  • Currently just "No Function"
• Modifier keys
  • Regular / Shift, option to add extras later
  • Shift also influences the MAVLink MANUAL_CONTROL outputs