This PR adds optional support for loading nccl with `dlopen` as an alternative of compile time linking. This is to address the size bloat issue with the PyPI binary release.
- Add CMake option to load `nccl` at runtime.
- Add an NCCL stub.
After this, `nccl` will be fetched from PyPI when using pip to install XGBoost, either by a user or by `pyproject.toml`. Others who want to link the nccl at compile time can continue to do so without any change.
At the moment, this is Linux only since we only support MNMG on Linux.
* Reduce clutter in log of Python test
* Set up BuildKite test analytics
* Add separate step for building containers
* Enable incremental update of CI stack; custom agent IAM policy
* [CI] Use RAPIDS 22.10
* Store CUDA and RAPIDS versions in one place
* Fix
* Add missing #include
* Update gputreeshap submodule
* Fix
* Remove outdated distributed tests
