Support PodGroup in scheduler-plugins/coscheduling

[zw0610]

At this moment, the training operator only supports PodGroup defined in volcano. Users are also using PodGroup defined in:

• scheduler-plugins/coscheduling

If there are other PodGroup definitions, let's added to this list.

We should make the PodGroup-related process more generic and let user choose PodGroup API in launch argument.

@denkensk @wsxiaozhang

[gaocegege]

/cc @kubeflow/wg-training-leads

[denkensk]

Great, this will be very convenient for users using default-scheduler/scheduler-plugins.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.