Mixer calibration routine

[Luca-Ben-Herrmann]

On 0.2 we currently do not have any routines for mixer calibration.

[andrea-pasquale]

Thanks @Luca-Ben-Herrmann for opening the issue.
Do you have something in mind already for the mixer calibration? Eventually we should think about some qibolab parameters that needs to be exposed to qibocal in order to calibrate them.