fix: include OTel semconv 1.20 attributes in spans

[robbkidd]

Which problem is this PR solving?

The 1.21+ HTTP attributes are not yet stable. Per the HTTP semantic convention v1.21/v1.22 guidance, we should send the "old" style attributes. Doing so will help the agent's telemetry play better with others when appearing alongside application instrumentation in the same set of services.

Short description of the changes

• Update handler to also include the v1.20 semconv attributes other OTel instrumentation is currently using so that existing queries match.

Proposed future followup:

• Add the OTEL_SEMCONV_STABILITY_OPT_IN flag for opting in to the new, as-yet unstable attribute names?

[robbkidd]

I reckon we can decide on whether/how to implement the OTEL_SEMCONV_STABILITY_OPT_IN flag in a followup!

I'll add some tests to expect these attributes to appear and then wrap up this PR as-is.

[robbkidd]

Might have gotten carried away with refactoring the code to make unit testing simpler. 😬

[MikeGoldsmith]

I like what your refactoring is doing. Maybe it could go one step further so the handleEvent func is responsible for creating the span, then we have handleHTTPEvent funcs that gather the specific event type attrs and the span name. This will make adding more event type handlers easier / cleaner.

Something like:

func handleHTTPEvent(event) (spanName string, attrs []attribute.keyvalye)

[robbkidd]

Maybe it could go one step further …

😈 You read my mind, @MikeGoldsmith, but I held off because I thought I was already going pretty far in this refactor.

I considered again having a handleHTTPEvent() return a span name and slice of attributes, but I think Not Right Now™. There's some http. attrs we set in the wibblyWobblyTimeyWimey getEventStartEndTimestamps() function. Maybe further handler logic separate can happen in a followup PR, maybe when we've got a second network protocol to handle.

[JamieDanielson]

This is great! I suggested a few more attributes to a test case but then I think this is good to go!

[JamieDanielson]

Also noting this table for quick reference, in preparation for docs updates:

"http.request.method" / "http.method"
"http.response.status_code" / "http.status_code"
"http.request.body.size" / "http.request_content_length"
"http.response.body.size" / "http.response_content_length"
"url.path" / "http.target"