Added RPC metrics collection for Apache Dubbo

[steverao]

Resolved #14611

[SylvainJuge]

Maybe there is a clear statement somewhere in semconv specifications, but I think there is a general pattern to capture all durations with seconds as unit, those related issues/PRs might be used as examples of this:

• Use seconds as default duration for DB client metrics semantic-conventions#381
• Semantic Conventions: default to seconds for duration units opentelemetry-specification#2977

[laurit]

Maybe there is a clear statement somewhere in semconv specifications, but I think there is a general pattern to capture all durations with seconds as unit, those related issues/PRs might be used as examples of this:

• Use seconds as default duration for DB client metrics semantic-conventions#381
• Semantic Conventions: default to seconds for duration units opentelemetry-specification#2977

Changing the unit would be a backwards incompatible change. We could add a task for 3.0 to change the unit for the rpc duration metrics.