[PT-D][Checkpoint]rename init() (#92829)
Fixes [#90346](https://github.com/pytorch/pytorch/issues/90346)
Rename init() method in planner to be set_up_planner() to avoid confusion between __init__() and init().
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92829
Approved by: https://github.com/kumpera