flash_attention integration (#81434)

# Summary:
- I added a new submodule Cutlass pointing to 2.10 release. The inclusion of flash_attention code should be gated by the flag: USE_FLASH_ATTENTION. This is defaulted to off resulting in flash to not be build anywhere. This is done on purpose since we don't have A100 machines to compile and test on.

- Only looked at CMake did not attempt bazel or buck yet.

-  I included the mha_fwd from flash_attention that has ben refactored to use cutlass 2.10. There is currently no backwards kernel on this branch. That would be a good follow up.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/81434
Approved by: https://github.com/cpuhrsch

setup.py

@@ -322,7 +322,7 @@ def get_submodule_folders():
     git_modules_path = os.path.join(cwd, ".gitmodules")
     default_modules_path = [os.path.join(third_party_path, name) for name in [
                             "gloo", "cpuinfo", "tbb", "onnx",
-                            "foxi", "QNNPACK", "fbgemm"
+                            "foxi", "QNNPACK", "fbgemm", "cutlass"
                             ]]
     if not os.path.exists(git_modules_path):
         return default_modules_path