Allow users to give their own background to the server (per server backgrounds)

### Is there an existing suggestion for this?

- [X] I have searched the existing issues before opening this suggestion.

### Describe your suggestion

As I work with a lot of custom projects it would be fun that every project even though they run on the same egg could have different backgrounds

### Describe the solution you'd like

Add a field below Server Information under settings where people can put an image URL in

### Additional context

_No response_

No files or tests are identified. Start by locating the Server Information settings view and the code that displays server backgrounds, then trace how settings are stored per server. Done means users can save an image URL for an individual server and see that background without changing other servers.

Written by the indexing model from the issue text.