Provide a config for a homeserver with animated media support

[salixor]

This provides a way to display animated media in the widget, by using a homeserver with a media repo which supports them.

It makes it possible to use one homeserver (which doesn't support such a media repo) for most of the thumbnails, and use one with support for the few animated media.

This is an optional config, which defaults to homeserver_url.

[tulir]

Why not just use the same one with proper thumbnailing support? 🤔

Could also not thumbnail for animated stickers, that way it works with all media repos

[LuckyTurtleDev]

Why not just use the same one with proper thumbnailing support?

This would be to easy.

[salixor]

The reasoning was to provide a way for people with no control over their homeserver (which may or not support such media repos) to have some configuration available to them.

Let's say their current HS supports animated thumbnails (it's nice to have them in the picker IMO) - but their HS is struggling. They switch to another one for thumbnails, but this one no longer supports animated thumbnails. They may want to display their stickers, and let the animated one load when they can.

I understand the best is to use the same HS in both cases, but having some additional configuration doesn't feel too irrational ! I'd understand if you don't want to merge it, I proposed this PR just in case it could be interesting for upstream as well o/

[YourSandwich]

Hello @salixor thank you for providing this code, I am interested in implementing this into my home server.