[DOC]: Design approach to CCCL documentation authoring

### 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

CCCL docs are lacking systematic approach. We have reference API fused with examples along with some accidental explanations and tutorials. Consequences of this lack of systematic approach include a) the fact that documentation for each overload is bloated, and b) user is lost when trying to learn how to use our libraries. We should design a systematic approach to authoring tutorials, how-to guides, explanations, and reference documentation across projects and languages. [Diátaxis](https://diataxis.fr/) might be a starting point.

### 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_