migrate off docker hub autobuild

[rongou]

Right now the deploy and example yaml files point to docker hub images built via their autobuild service, but Docker is turning off that service on June 18th, 2021, so those images won't be updated after that. Need to find an alternative to build these images:

mpioperator/mpi-operator
mpioperator/tensorflow-benchmarks
mpioperator/kubectl-delivery
mpioperator/mxnet-horovod

@terrytangyuan

[terrytangyuan]

@kubeflow/wg-training-leads @PatrickXYS Is there shared infra that can be used for this?

[gaocegege]

cc @Jeffwan

[yindia]

@terrytangyuan @rongou should we use GitHub workflow for publishing these images in GitHub registry ?

[terrytangyuan]

I think new images will be released as part of https://github.com/kubeflow/training-operator.