* Stage multi-arch awx image
- change CI to use `make awx-kube-build` instead of build playbook
- update staging CI to build and push multiarch awx image
- update doc to use `make awx-kube-build` to build awx image
- remove build playbook (no longer used)
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
