[DOC][STF] Document dot sections

[caugonnet]

Is this a duplicate?

• I confirmed there appear to be no duplicate issues for this bug and that I agree to the Code of Conduct

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

Update

Describe the incorrect/future/missing documentation

To reduce the amount of graph nodes in the DOT files generated by CUDASTF, we have introduced "dot sections", which are either available using an RAII API, or with a push/pop API.

• We need to document how to use them in applications
• We need to document/illustrate how this affects the generated DOT
• We must document the CUDASTF_DOT_MAX_DEPTH environment variable and define default behavior

We can use the example currently in cudax/test/stf/dot/sections.cu to illustrate this on actual DAGs.

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.

https://nvidia.github.io/cccl/cudax/stf.html