Review Kafka and RabbitMQ attributes

[lmolkova]

Based on the messaging SIG discussion on 2/15/24, we should target stabilizing Kafka and RabbitMQ semconv along with the messaging semconv stability.

While we can always add span attributes, but adding attributes to the metrics is breaking #722.

So prior to stability, we should

• review if some important (for metrics) attributes are missing
• have kafka and rabbitmq metrics instrumentation prototypes

Update: see https://github.com/open-telemetry/semantic-conventions/pull/798#discussion_r1516427699

• we should also check rabbitmq/kafka attributes to see if any of the existing ones are good candidates to be generalized