Add and use new ModeReason::AUX_FUNCTION

[IamPete1]

Aux function are no longer only from RC. This changes to use a dedicated mode reason.

We don't check for the old ModeReason::RC_COMMAND anywhere in the main code. Nor is it exposed over MAVLink. There is a scripting binding, and it is used in logging.

The scripting binding is vehicle:get_control_mode_reason(), it is not used by any of our examples.

[peterbarker]

@IamPete1 we could, perhaps, have multiple AUX_FUNCTION enumeration entries, and choose a different one based on AuxFuncTriggerSource - as you say, there are many ways we can trigger aux functions now-adays.

[IamPete1]

@IamPete1 we could, perhaps, have multiple AUX_FUNCTION enumeration entries, and choose a different one based on AuxFuncTriggerSource - as you say, there are many ways we can trigger aux functions now-adays.

We also have AUXF log, so this mode reason should be enough to tell you to go and look at the AUXF where the source is logged.

[rmackay9]

I'm fine with this solution or PeterB's suggestion.