Deprecate on_configure_sharded_model callback hook for v1.6

[Piyush-97]

What does this PR do?

Fixes #11560

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

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Did you have fun?

Make sure you had fun coding 🙃

[ananthsub]

Please add an entry to the CHANGELOG as well. Thanks again for working on this!

[daniellepintz]

LGTM!

[tchaton]

LGTM after applying comments.