Option to fix position of prev/next buttons in diff view

Proposal

This is a simple browser-side UI proposal which results in less hassle while navigating large merge requests.

When viewing diffs in merge request with multiple files, there are < Prev | Next > buttons below the diff (if we are viewing single file at a time). Because diffs have different height, these navigation buttons jump up and down and you have to find them every time you switch the file.

Currently i use custom CSS which fixes them in one place and makes a bit transparent.

CSS is very simple and i had no issues with it so far:

[data-testid="file-by-file-navigation"] {
  position: fixed;
  bottom:0%;
  left: 50%;
  background-color: #ffffff66;
}

It would be nice to have this as an option somewhere!