gifs versus mp4 instance level toggle

[ghost]

So, currently, mastodon uses MP4s for all gifs in post content. this was a change made to master to conserve file storage space, that has a lot of downsides (shown below)
-lossy conversion that makes many gifs unreadable
-unable to easily download the animation to share without using an external site
and one upside
-less file space used on server
This said, avatars already support all the features we want accessibility wise from animated images using standard gifs, and thus all the upsides of gifs (quality, easier sharing and reuse/discover media by others) and thus any server could come to support gifs as an instance side option to opt-in to the more powerful features at expense of storage space.

as such, I propose admins be able to swap between the two options, namely 'convert uploaded images to mp4' and 'full quality'

this can probably federate as is, but we could go even further and allow an opt-out on the federating level to allow recieving instances to Not locally store the gif, (thus dynamically loading into frontend) or to federate them to instances that prefer mp4s as mp4s converted for the sake of federation