Primary changes are:
- Generalized variable names (remove "docker")
- Add explicit "push" variable rather than checking if the "registry" variable is defined.
- Allow for passing in version as build arg
This does a few things:
- Removes need for awx_sdist_builder image
- Reorders Dockerfile steps to optimize image cache between prod and dev builds
- Unifies VENV_BASE and COLLECTION_BASE in prod and dev builds