Resolve "Adding cover art to my albums"

Closes #588 (closed)

This leverages !951 (merged) and implement the API/front-end to update cover art on albums:

• Backend logic to support suggesting a new album cover (a.k.a mutations)
• Front-end logic to suggest new cover
• Handle cover update over federation

cc @funkwhale/reviewers-python

Demo

album-cover-update