Accepting a merge request for a cherry-pick should by default remove the source branch.

Description including problem, use cases, benefits, and/or goals

Right now, whenever we create a cherry-pick merge request, when we go to accept the merge request, we have to remember to click the "remove source branch" checkbox. This leaves us with a bunch of old branches because we use the feature a lot - various people - and some will forget. We'd like to avoid that.

Proposal

If a souce branch follows the cherry-picks-shorthash naming convention, the "remove source branch" checkbox should be checked by default.

~"feature proposal"