Allow user to define a "prefix" for the branch slug for request-review

[jameswalmsley]

I'd like to be able to set a "prefix" to the branch slug that gets pushed up for review.
In our org we are supposed to prefix our own branches with e.g. wip/jw/my-branch-for-a-pr

[drewdeponte]

Interesting.

Right now you can specify the branch name when you use the rr or the branch command to be whatever you want.

We could probably add a configuration option of branch_slug_prefix which would default to ps/rr/, but could be configured to whatever you want.

[drewdeponte]

It would probably be the first config option that would span across commands though. So we would probably have to figure out how we want to clearly define that in the config files.