Feature request: Show merge SHA in MR widget after merging

It is often helpful to be able to quickly see the commit SHA of a merge that was made by a successful merge request.

1. You could click on it to see the pipeline that was run post-merge.
2. Release managers can use it to easily find the SHA they need to pick a merge into a stable branch.
3. If someone wants to manually revert a MR (i.e. not through the buttons in the MR widget), they can use the SHA string to find the diff.

In the case of a normal merge, this SHA should be the merge commit. If it was a rebase + fast-forward merge, it should be the SHA of the last commit. If it was a rebase + squash merge, it should be the SHA of the squashed commit applied to the target branch.

We could place it here:

(optionally with the type of merge indicated)