use the tracing event name as the otel event name

[zzlk]

Motivation

When using the tracing macros and trying to explicitly set the 'name' of the event, for example:

event!(name: "test", Level::INFO, field1 = "field1");

This event will get emitted to open telemetry as an event with an empty name. The 'name' information will be completely lost. It seems common for this information to get dropped actually, see: tokio-rs/tracing#2774

Solution

In on_event I set the event name to event.metadata().name() which should be the name of the event that is handed down from tracing. I am unfamiliar with this code and the wider tracing/opentelemtry ecosystem so I am not sure this is a good way to solve this issue, or if this is even a real issue. I am also not sure what this change would break, and what kind of backward compatibility guarantees there might be. I have tested my use case (sending traces/events to jaeger) and can confirm that the names of events are being recorded correctly with this change.

[djc]

I think this might make sense.