ci: add container build

[khassel]

This is a draft PR for creating the container image in this repo.

We have to discuss if we want to move the build from gitlab into this repo.

I created an image on my fork which works:

• image: docker pull ghcr.io/khassel/magicmirror-3rd-party-modules:main
• job log

I'm not really convinced of github actions but it would be a cleaner setup to do the build here.

Disadvantages (so far):

• github actions cron has still no timezone support

[KristjanESPERANTO]

I am open to all options. But yes, it appears to be cleaner to do the build here 🙂

[khassel]

so let us merge this ...

After merge and first successful build I will change to the new image (build here) in our mm-server setup.