Adding release compatibility matrix for release 2.1 (#106891)
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### <samp>🤖 Generated by Copilot at 3c5a179</samp>
Update `RELEASE.md` with compatibility information for PyTorch 2.1. This file documents the supported versions of Python, CUDA, and CUDNN for each PyTorch release.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106891
Approved by: https://github.com/kit1980
