Add gates.GeneralizedRBS gate

[renatomello]

This needs qiboteam/qibojit#183

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.94%. Comparing base (37e1010) to head (3e83876).
Report is 46 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1373   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          78       78           
  Lines       11236    11297   +61     
=======================================
+ Hits        11230    11291   +61     
  Misses          6        6           

Flag	Coverage Δ
unittests	99.94% <100.00%> (+<0.01%)	⬆️

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[MatteoRobbiati]

Thanks, LGTM!

[renatomello]

@scarrazza @MatteoRobbiati the PR in qibojit needs to be merged before this one