Make visiting a merged MusicBrainz entity HTTP redirect to its new target
Currently in MusicBrainz when two (or more) entities get merged, they all "live" under the same MusicBrainz identifier, but visiting the entity using its old identifier won't tell the browser that they're on the wrong page, but happily serve up the content.
E.g., visiting https://musicbrainz.org/artist/f21a407e-3af9-4539-ab3d-c92a5230dff6 and https://musicbrainz.org/artist/1155431a-d35e-4863-9ae0-e3c24eb61aa9 show you completely identical pages, so the goal of this task is to make visiting the former cause a HTTP redirect to the latter.
Once completed, submit a pull request with your changes to the GitHub repository, and respond to any suggestions and requests by the MusicBrainz developers until the pull request is approved (you do not need to wait until it gets merged).