Add pusher assist mode above MPC_LAND_ALTx (except LANDING).

[sanderux]

Adding 2 new modes for VT_FWD_THRUST_EN to enable activating pusher assist when above MPC_LAND_ALTx AND not during a landing stage.

Reason:

Some vtols, given enough wind, can generate too much lift with pusher assist for a stable landing. Hence during landing it should be disabled. Also for precision landing it should disable when close to the ground (some pushers can hit the ground)

[sfuhrer]

Also for precision landing it should disable when close to the ground (some pushers can hit the ground

I guess in that case you also want it disabled in takeoff if below some altitude, that's why I didn't add a specific case for the landing.
I personally haven't experienced a case where lift due to wind didn't allow it to descend, but if it is a real thing in more windy areas with airframes with a lot of wing area then I'm fine to add these options. For consistency we should do also add it to the "Enable FW forward actuation in hover in altitude, position and auto modes." case in my opinion.

[sanderux]

I guess in that case you also want it disabled in takeoff if below some altitude, that's why I didn't add a specific case for the landing.

Takeoff already disables navigation below mpc-altx so it never reaches the minimum pitch value, hence its implied not to activate pusher assist in the first meters.

I personally haven't experienced a case where lift due to wind didn't allow it to descend, but if it is a real thing in more windy areas with airframes with a lot of wing area then I'm fine to add these options. For consistency we should do also add it to the "Enable FW forward actuation in hover in altitude, position and auto modes." case in my opinion.

Airframes with some pitch offset in the wing have this. It makes descend unstable.

Not sure what you mean with the last bit

[sanderux]

@sfuhrer any thoughts on this?

[sfuhrer]

Takeoff already disables navigation below mpc-altx

It doesn't change a lot in the context of this PR, but I don't think that's exactly the case. There is a tilt angle limitation which is tighter when still in the ramp-up process, but there is no complete disablement of the pusher assist during takeoff if you don't do the enabling based on altitude.

Not sure what you mean with the last bit

My bad, didn't notice that it's already covered by value "1".