push extra_tag to registry

[Raboo]

Describe the Feature You Want

I want docker_build()'s extra_tag to be pushed to the registry, now it's only the $EXPECTED_REF that is pushed.

Current Behavior

extra_tag is only local, not pushed to registry.

Why Do You Want This?

I want to have tags in the registry that I can revert to and know which tag is the previous. I want to have human readable tag names in the registry. I want to use tilt in a ci pipline that runs for production as well, not just development. For production it's more common to create versioned tags.