Build Docker images and publish on registries

[jbg]

Build multi-arch (at least x86_64 + arm64) Docker images and publish on Docker Hub and other registries.

[daimoc]

Hi @jbg, have you plan to publish some gst-meet docker images now that gstreamer 1.2 is present in stable Alpine version ?
I have made a pull request some day ago with a little modifications in the docker file to build a running image.
Regards.