Two-step merge request widget
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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 |  |
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