Also provide docker images through github registry

[yamalight]

Docker is changing some policies on how images from free users are stored (and how free consumers can pull them), so it'd be good to have a backup in form of images in github registry.
Shouldn't be too hard to setup.
Don't forget to update docs to point to those images as well.

[yamalight]

Just in time: Introducing GitHub Container Registry

[yamalight]

Updated docs: https://docs.github.com/en/packages/working-with-a-github-packages-registry

[yamalight]

Since docker is doing weird stuff again - old exoframe/server images are now available on github.
At this stage should probably drop docker hub completely as it became unpredictable.