Display source branch name in merge request sidebar

Problem to solve

When reviewing code changes, discussions, and commits in a merge request, it is often desirable to checkout the branch locally for a more in-depth review. However, finding the branch name becomes harder as more content is added to the merge request description as more scrolling is necessary.

The branch name has now been added to the merge request sidebar, making it easily accessible at all times and removing the need for scrolling. Just as the merge request reference, the source branch section provides a convenient "copy" button for easy local checkout.

Many thanks to Ethan Reesor for this great contribution.

Further details

The merge request view ("/merge_requests/51") should permanently show the corresponding remote branch name, even when working/scrolling through the discussion, the commits or the file changes.

Proposal

Show the branch name related to a merge request in the request view's right hand sidebar, where other related data is shown (assignee, participants, merge request URL etc.).

What does success look like, and how can we measure that?

Success: The user is able to copy the merge request's branch name, independently of where in "/merge_requests/51" she is scrolling to.

Links / references

(none)