Two-step merge request widget

This may not be a very common problem, but I've accidentally accepted a merge request in the past. If we had a confirmation of some sort, this could be avoided.

We could have the widget change to a new state when you click Merge that would let you edit the commit message and show a different button to confirm the merge.

Things to think about:

• How would this work with slash commands? Would /merge bypass the second state completely? Presumably if you type that explicitly, you are definitely sure you want to merge

Design mockup

Step	Mockup
Ready to merge - idle
Ready to merge - confirmation step