MC autotune: change signal input to sine sweep

[bresch]

Solved Problem

In some cases, the gains obtained by auto-tuning weren't good enough because the system identification wasn't able to capture the dynamics properly.

Solution

One possible cause of a poor model identification is when the dominant dynamics are not correctly excited.
This PR changes the current doublet input signal to sine sweeps (as suggested by Ryan Beall). As they cover a wider range of frequencies, they give a higher chance to correctly capture the system dynamics.

The current implementation is also more generic and other signal types can be added.

Changelog Entry

For release notes:

Changed MC autotune input signal from doublets to sine sweep
New parameter: MC_AT_SYSID_F0, MC_AT_SYSID_F1, MC_AT_SYSID_TIME, MC_AT_SYSID_TYPE
Documentation: Need to update autotune page

Test coverage

SITL tests for now

[MaEtUgR]

Dev call: Change to have multi-step by default. Then merge refactor and test both.