Summary:
Expose nlohmann json library so that it can be used from inside Pytorch. The library already exists in the `third_party` directory. This PR is making `nlohmann/json.hpp` header available to be used from `torch.distributed`.
The next PR makes actual use of this header.
imported-using-ghimport
Test Plan: Imported from OSS
Reviewed By: malfet
Differential Revision: D59035246
Pulled By: c-p-i-o
Pull Request resolved: https://github.com/pytorch/pytorch/pull/129570
Approved by: https://github.com/d4l3k, https://github.com/malfet