Mavsdk: Add position control to offboard

[julianoes]

Offboard currently only supports velocity inputs, however, it would be good to also have position control.

[hamishwillee]

Yes! I think we need to consider whether we can make this simpler than velocity control. For example, should DC handle the resending of messages? I would say yes.

It might also be nice to have an API that completes when you reach the destination.

[julianoes]

Being addressed by #260.

[afwilkin]

Hello, I was looking for something similar to this (a method like set_velocity_body()) under offboard mode. Is this still being developed?

[julianoes]

This is done.

See: https://github.com/mavlink/MAVSDK/blob/7d7579659f8c12e3d9406a17eac96f3382153a5b/src/plugins/offboard/include/plugins/offboard/offboard.h#L208-L213

[hamishwillee]

And here in the docs

[Iko-Git]

Could you please give me a guideline for using _float mavsdk::Offboard::VelocityBodyYawspeed::forward_m_s {}_ into _ROS_
or generally velocity control of the vehicle locally into _ROS_ @hamishwillee @julianoes

[julianoes]

@Iko-Git please don't necrobump and create a new issue.