[enhancement] Add SchedulerName in V1alpha2

[gaocegege]

We have the gang scheduling option while we do not support schedulername for TFJob, and we should add it to keep consistency with v1alpha1.

[gaocegege]

/assign @ChanYiLin

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[ChanYiLin]

/assign @ChanYiLin

[k8s-ci-robot]

@ChanYiLin: GitHub didn't allow me to assign the following users: ChanYiLin.

Note that only kubeflow members and repo collaborators can be assigned.
For more information please see the contributor guide

In response to this:

/assign @ChanYiLin

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ChanYiLin]

/assign @ChanYiLin

[gaocegege]

Close by #787, some discussions are in here #801