[DOC] Add documentation and examples for nestedSetLeft/Right/Parent

[knylander-grafana]

Update the TraceQL documentation to include nestedSetLeft/Right/Parent in the Intrinsics section: https://grafana.com/docs/tempo/next/traceql/#selecting-spans

This capability was added in the 2.5 release.

Provide examples of usage.

Questions to answer:

• What is the use case for when this intrinsic would be good in a query?
• Why would someone use this? (use case/benefit)
• What are some basic and more complicated examples that show a real-world use case?

[louislepper]

A key use case that I'm looking for (not yet sure if TraceQL intrinsics will do this for me) is:

Root Span -> ... various spans ... -> Service A span with userId attribute -> ... various spans .. -> Service B -> Service B inner span -> Other spans...

Service B inner span could be a particularly slow or expensive method, for example.

I want to get a list of all users who hit "Service A span" who also hit "Service B inner span".
The ideal output would look like:
UserId | Count
1234 | 2000
5678 | 5
...

The count should not include times that "service B inner span" was hit not via "Service A span".

Thanks

[mapno]

Are you familiar with structural operators? They should cover most of what you're trying to do.

Root Span -> ... various spans ... -> Service A span with userId attribute -> ... various spans .. -> Service B -> Service B inner span -> Other spans...

{ nestedSetLeft<0} >> { resource.service.name = "service-a" } >> { resource.service.name = "service-b" } > { resource.service.name = "service-b" && kind = internal } > { .foo = "bar" }

A query like the above should get you that. Depending on the specifics of your traces.