Add cuGraph examples

We currently have a pretty extensive list of graph storage and processing approaches on the CPU, but lack GPU analogs. This can be a great opportunity to showcase both the more advanced and rarely used parts of the Nvidia libraries, as well as explore atomic variables and concurrent data-structure implementations on massively parallel chip architectures.

- [cuGraph C++ docs](https://docs.rapids.ai/api/cugraph/nightly/graph_support/cugraph_cpp_support/)
- [PageRank C++ docs](https://docs.rapids.ai/api/cugraph/nightly/graph_support/algorithms/cpp_algorithms/centrality_cpp/#Pagerank)

This is also worth covering on the [Python side](https://github.com/ashvardanian/less_slow.py) with the available Python cuGraph bindings:

- [PageRank example Jupyter notebook](https://github.com/rapidsai/cugraph/blob/main/notebooks/algorithms/link_analysis/Pagerank.ipynb)