] Add python impl of sdpa_with_kv_cache (#2153)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2153

This change will allow model rewrite in eager model to use sdpa_with_kv_cache.
ghstack-source-id: 216744337
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validated oss ci is clean. have to by pass because ci think its needs internal linter to pass.

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Reviewed By: mergennachin

Differential Revision: D54075829

fbshipit-source-id: ba1a3a89f294d9ffe860dc40d181dcd7ba01a23d