Dynamically update ff gain for fw rate control

[Jaeyoung-Lim]

Solved Problem

For fw_rate control, the feedforward term was being computed outside the rate controller.

Solution

This is an aesthetic change that modifies the feedforward gain of the fixed-wing rate controller, rather than adding a separate feedforward computation outside the rate library.

IMHO, this makes it a little bit more clear how the feedforward gain is being computed.
(Saves one vector multiplication and one vector addition :P)

Changelog Entry

For release notes:

Feature/Bugfix Dynamically update feedforward gains, in the fw_rate_control instead of computing feedforward inline.
New parameter: None
Documentation: Dynamically update feedforward gains, in the fw_rate_control.

[bresch]

Why not, yes. Next step would be to move the dynamic pressure scaling to the control allocator (as this changes of the actuator effectiveness)

[Jaeyoung-Lim]

@bresch Thanks!

Yes, I am looking into tracking acceleration using iNDI, which would require us to do metric allocation.