.github/workflows/build: enable pushing to dockerhub

[classabbyamp]

despite dockerhub's checkered recent past, I think this is beneficial, especially as alpha.de's DNS no longer works, breaking people who use the current dockerhub container as-is. If we do this, we should be able to remove the old images and direct people to the new ones.

This will require dockerhub credentials be added as secrets.

[classabbyamp]

we should also consider removing the old ghcr images so people migrate to the updated ones:

• https://github.com/orgs/void-linux/packages/container/package/void-linux
• https://github.com/orgs/void-linux/packages/container/package/docker-bootstrap

[leahneukirchen]

Perhaps explicitly mention docker.io (iirc), so it's clear where it pushes.

[Anachron]

Is there a discussion I missed which speaks against merging this?

[classabbyamp]

not really

[Anachron]

Still not sure why this is not being merged.

Is this just a "lets wait if something comes up against it" or do we actually need someone else to approve it?

[classabbyamp]

probably because we've been doing other things