Migrate away from DockerHub

[lunik1]

Docker Hub is disabling autobuilds on the free tier on 2021-06-18 so we need to look at moving to an alternative container hosting platform.

Currently a GitLab mirror of tt-rss with and a webhook on push events is used to trigger container rebuilds, as well as any pushes to this repo (which is linked to the image on dockerhub). Something that this setup can be easily migrated to would be ideal.

I'm not too familiar with the alternatives, so is any users have feedback/ideas I'd like to hear it! Frontrunner is ghcr as this would bring us in line with lsio these days.

[lunik1]

This repository and containers are moving to GitLab.

[lunik1]

For most users, all you should need to migrate is change the image location to registry.gitlab.com/lunik1/docker-tt-rss