Add TensorPipe header files to Python package (#105521)
This change adds the TensorPipe header files to `torch_package_data` if `USE_DISTRIBUTED` is set to `ON` in the CMake cache. The TensorPipe library and CMake config is already available in the Torch wheel, but the headers are not. This resolves issue where out-of-tree backends could not implement TensorPipe converters, because the definition of the `tensorpipe::Message` struct is defined in the TensorPipe headers.
Fixes #105224.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105521
Approved by: https://github.com/albanD
