Support distributed tracing across Pub/Sub

[EricStG]

Is your feature request related to a problem? Please describe.
I want to be able to correlate distributed traces for requests sent over pub/sub

Describe the solution you'd like
Ideally, support for OpenTelemetry that will:

• Create a new activity when sending/receiving messages
• Enrich pub/sub messages with the attributes for correlation / baggage propagation

Describe alternatives you've considered
We're doing it manually for now with the OpenTelemetry propagators.

Additional context
Similar to #8366, but we haven't had issues with automated instrumentation over HTTP, but pub/sub is a big blindspot for us.
Sounds like there are internal discussions around supporting this over different languages like golang and nodejs, but can't tell how far those discussions have gone

[jskeet]

Assigning to Amanda for comment as she knows more about OpenTelemetry than I do. (But fundamentally I wouldn't expect to see anything here soon.)

[amanda-tarafa]

@EricStG Yes, there are ongoing discussion to support OpenTelemetry for all libraries, inlcuding Pub/Sub, across all languages, including .NET, but those are on very early stages. As @jskeet said, don't expect anything soon.

It seems you already have implemented tracing manually, so this might no be useful for you, but you can use Google.Cloud.Diagnostics.Common to add tracing to non-HTTP contexts. Apart from the linked docs, see #5897 and #6367 for more context. And of course, create specific issues if you have questions or run into problems.

If it's OK I'd prefer to close this issue as a duplicate of #8366 as we are including Pub/Sub in all our explorations.