New quick action to "Remove source branch when merge request is accepted."

Description

I totally love the slash commands that were added in gitlab 8.11 (am I right on the version number) and I love using them when creating a MR. You can set with them the Assignee field, the Milestone field, the label field. There is one I also constantly use, it's the Remove source branch when merge request is accepted. checkbox. I would love to be able to check it with a slash command instead of using my mouse…

Proposal

I suggest to introduce a slash command similar to

/remove_source_branch

Links / references

See the list of available slash commands.