RFC: reviewer management, e.g. lab reviewer --add --remove --require

[camuso]

The request is to add the ability to add and remove reviewers in an MR.

For example:

lab mr reviewer --add mumble,sprotz,hust ... adds reviewers mumble, sprotz, and hust to the mr.

lab mr approver --add aus ... adds aus as an approver to the mr

[camuso]

OK, this is already there, mostly.