Add migration guide from Training Operator to Kubeflow Trainer V2

[andreyvelich]

Ref: #2170

We should add user guide on how to migrate from Kubeflow Training Operator to Kubeflow Trainer V2.

cc @varodrig

/area docs
/good-first-issue

[google-oss-prow]

@andreyvelich:
This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-good-first-issue command.

In response to this:

Ref: #2170

We should add user guide on how to migrate from Kubeflow Training Operator to Kubeflow Trainer V2.

cc @varodrig

/area docs
/good-first-issue

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.

[akagami-harsh]

/assign