feat: add support for pushing to Docker Hub

[owenvoke]

Description

Add a flag that pushes to Docker Hub automatically.

As suggested by @rsinnbeck on Twitter.

Possible implementation

For example, the flag could be php application app:docker --publish, which would just run docker push behind the scenes.

But need to think about how to provide things like user/repo details, tags?, and I guess remotes as well (for example if pushing to Docker Hub and GitHub Container Registry).