Introduce hydra framework with backwards compatibility

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This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #11029 by @jackzhxng
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ghstack PR base: https://github.com/pytorch/executorch/tree/gh/jackzhxng/11/base
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Merge bot PR base: https://github.com/pytorch/executorch/tree/gh/jackzhxng/10/orig
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/jackzhxng/11/orig
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