Support manual instrumentation

[einepeople]

Support registering Beyla as global tracer provider, so that it can support manual instrumentation and link manually created spans with auto-generated traces.
Such functionality exists in opentelemetry-go-instrumentation since late 2023.

Without manual spans support every user request generates two completely disconnected traces - one with manually defined (e.g. business logic oriented) spans, and one with auto-generated spans (which only describes app's external communication).

Reference:

• Issue with description: Add manual instrumentation support opentelemetry-go-instrumentation#352
• MR with impl: Manual instrumentation support - Phase 1 opentelemetry-go-instrumentation#523

P.S. there is a similar issue opened for grafana/beyla. I heard the community should now contribute to this repo and not to the beyla. If that's not the case and this is a duplicate issue, feel free to close it.

[marctc]

Thanks for reporting. Yeah, this would count as duplicated issue, so we can close it (eventually we would many of the Beyla issues here). However you provided some context here that I will link in the other issue. Thanks!

[grcevski]

There's enough context here @marctc ! We need Go SDK support for manual spans.