Option To Select GIF Provider (And Add Stoat's New GIF Provider: Gifbox)

Problem

Currently Fluxer has just one GIF provider(KLIPY), but perhaps there there should be another one to choose from. Extreme hypothetical, but what if KLIPY goes like Tenor and shuts down? We'd need a backup in place. Even without that concern, it'd be good to help out Stoat's new GIF provider by contributing to its GIF selection.

Proposal

We should have the option to choose another GIF provider to search from. I suggest the alternative to be Stoat's new GIF search system, Gifbox. https://stoat.gg/meet-gifbox Much like how other settings on Stoat allow you to select alternatives, such as reverse-image search, or translate system, we should have a similar setting to choose GIF providers, but perhaps this should be accessible from the GIF search menu, to switch where to search from.

Notes

I've heard that Fluxer used to have this option to choose between Tenor and KLIPY before Tenor's API shut down, so there is already a precedent for an implementation of this suggestion.