🚀 Feature: Ability for users to set a profile picture

[acidRain-burns]

Feature description

Allow users to set and change their profile picture, and allow this to be provided to client applications when requested. A simple input like what is already offered for OIDC Client settings should suffice. If it makes more sense or is too much overhead, allowing users to set their own URL or letting server owners set their own avatar service might be a better option.

Pitch

There are many client applications Pocket ID is working really well for, and many of them have profile picture imports. It would be nice for people to be able to set their picture once, and have it show up everywhere without them or I needing to mess with Gravatar (though the inclusion of Gravatar is a great feature!).