Deprecate TrainerCallbackHookMixin

[daniellepintz]

What does this PR do?

In #10575 I removed many methods of TrainerCallbackHookMixin, but we should keep them for BC until v1.8 so that Trainer.call_hook still works as it did before, i.e. if someone calls Trainer.call_hook("on_before_accelerator_backend_setup") that should still work.

This PR puts back the methods removed in #10575, and then deprecates the entire TrainerCallbackHookMixin class.

Does your PR introduce any breaking changes? If yes, please list them.

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Make sure you had fun coding 🙃

[tchaton]

LGTM !

[Borda]

still draft?

[daniellepintz]

@Borda I am waiting for #11179 to be merged first

[daniellepintz]

Ready to be merged!