Add Sageattention Codes as a tutorial

[jt-zhang]

New contributor declaration

• [x] I am not making a trivial change, such as fixing a typo in a comment.

• [x] I have written a PR description following these rules.

• [x] I have run pre-commit run --from-ref origin/main --to-ref HEAD.

• Select one of the following.

  • [ ] I have added tests.
  • /test for lit tests
  • /unittest for C++ tests
  • /python/test for end-to-end tests
  • [x] This PR does not need a test because this is a tutorial file.

• Select one of the following.

  • [x] I have not added any lit tests.
  • [ ] The lit tests I have added follow these best practices, including the "tests should be minimal" section. (Usually running Python code and using the instructions it generates is not minimal.)

SageAttention is a 8-bit attention that achieves speedups of 2.1x and 2.7x compared to FlashAttention2 and xformers, respectively, without losing end-to-end metrics across various models. This PR provides the official implementation, and we have verified the correctness of the codes.

[ThomasRaoux]

This would belong https://github.com/triton-lang/kernels repo instead

[Jokeren]

I agree that it's not a good fit