Improve instrumenter logging

[grcevski]

Not finding all components that we can instrument in an application is normal. For example, we may find symbols related to http.Serve, but no symbols for gRPC. At the same time, it would be good to show what components (features) we managed to instrument in an application.

• This PR changes few Warn messages to Debug, related to not finding certain symbol offsets.
• This PR also prints which features we instrumented in a given application.

For example, on start we'd print this for our integration tests server with INFO logging:

time=2023-04-20T10:46:36.076-04:00 level=INFO msg="creating instrumentation pipeline"
time=2023-04-20T10:46:36.270-04:00 level=INFO msg="instrumented features ['go runtime','http server','grpc server']"
time=2023-04-20T10:46:36.271-04:00 level=INFO msg="Starting main node"

If we try to instrument our pingserver test application, we'll only print a subset, e.g no 'grpc server':

time=2023-04-20T10:46:36.076-04:00 level=INFO msg="creating instrumentation pipeline"
time=2023-04-20T10:46:36.270-04:00 level=INFO msg="instrumented features ['go runtime','http server']"
time=2023-04-20T10:46:36.271-04:00 level=INFO msg="Starting main node"

[grcevski]

Thanks Mario!