Provide alternative docker registry

[Dev25]

Quay.io hasn't had the best uptime this year, allow users to pull from dockerhub or perhapsgithub pkg as a alternative

[sagikazarmark]

I'd be happy to provide a gihub alternative with a GitHub actions CI flow. Alternatively, pushing to both GitHub and DockerHub could be an option.

[Dev25]

So i had a play around with using Github Actions/Packages (thanks for your modern-go-application sample repo!)

https://github.com/Dev25/mcrouter_exporter/packages/274062

Unfortunately i also realised that you can't pull from github packages unless you authenticate first.
I'm happy to keep publishing images to GH but i don't see that getting much usage until that's fixed. I'll look into pushing to Dockerhub.

[Dev25]

Github Actions/Packages support is added in #18, will wait until we have Dockerhub support to close out this issue.

[sagikazarmark]

Setting up Docker Hub is trivial IMHO, now that they support personal access tokens you don't even have to use your login credentials anymore. Added an example in the linked PR for a docker hub setup.