Add semantic convention for code.function and code.namespace

[doppleware]

Description

Similar to the OTEL agent, for the @withspan annotation and JAX-RS endpoints add the semantic conventions
code.function and code.namespace

Use cases

I want to be able to track the trace back to the code and understand which class the span or endpoint is at

[Emily-Jiang]

It is a good idea but the design is still experimental. Let's wait till it is stable and then support this.

[Emily-Jiang]

We can discuss in the next call to see whether the new design is stable or not.

[Emily-Jiang]

At today's call, it seems that the code.function is stable at the Semantic Convention release 1.33.*+ (see here).

[Emily-Jiang]

We need to support the attributes documented here

[Emily-Jiang]

@Yas-Franco will do some experiments and report back on the next call.

[Emily-Jiang]

The attributes documented here are the good candidates for this.