Fully customizable OpenTelemetry Instumenter beans

[lgathy]

Make OTel Instrumenter beans fully customizable via their factory methods

[lgathy]

@n0tl3ss This draft exposes all customizations available on the OpenTelemetry InstrumenterBuilder-s by injecting them as beans in the factory methods. This way it is easy to add new client or server metrics, or replace the SpanNameExtractor-s, etc. Could you please take a look to see if this is a viable approach? I haven't added test just yet.

Another question I had: I saw that all beans defined in these factories are declared as @Prototype, but I couldn't quite figure out why that's needed. If I understand correctly, the Instrumenter object does not have any mutable state, as far as I can tell, every bean could be @Singleton, no? For now I added the new ones as singletons, but I'm keen to hear if you think that could be the case for all the existing beans in here as well. Thanks.

[n0tl3ss]

Hi @lgathy I think you are right that @Prototype should be changed to @Singleton. Everything else looks ok to me. :)