Add support for pushing to container registries different than Dockerhub

[andreriesco]

Signed-off-by: Andre Riesco andre.riesco@toradex.com

[microhobby]

@andreriesco also take a look at the TCB template, because some common stuff is not done there, and will possibly need an adjust. Let me know.

[andreriesco]

For tcb it was still missing. I fixed it and rebased the code, now it is working also for the tcb-platform-publish and tcb-platform-publish-ostree commands

[microhobby]

LGTM