[DOC]: Document `cub::WarpExchangeAlgorithm`

### Is this a duplicate?

- [X] I confirmed there appear to be no [duplicate issues](https://github.com/NVIDIA/cccl/issues) for this bug and that I agree to the [Code of Conduct](CODE_OF_CONDUCT.md)

### Is this for new documentation, or an update to existing docs?

New

### Describe the incorrect/future/missing documentation

https://github.com/NVIDIA/cccl/pull/256 introduced shuffle-based warp exchange algorithm. There's currently no documentation on `cub::WarpExchangeAlgorithm` enum. We need documentation and code samples to illustrate algorithms requirements and usage.

### If this is a correction, please provide a link to the incorrect documentation. If this is a new documentation request, please link to where you have looked.

_No response_