Create a CCCL demo project

[jrhemstad]

We want to steer people towards using cmake as the canonical path for using CCCL from GitHub.

We should provide a simple, standalone example project that shows how to:

• Get CCCL from GitHub
• How to link CCCL against a user application/library in cmake
• Compile/run some code using CCCL + cmake

I think this example project should be based around using CPM to fetch CCCL from GitHub.

Examples from other projects:

• https://github.com/rapidsai/cudf/tree/branch-23.08/cpp/examples/basic
• https://github.com/NVIDIA/nvbench_demo