Add `peer.service` for kafka related instrumentation's Producer spans

[ericmustin]

Following up on https://github.com/open-telemetry/opentelemetry-ruby/pull/978, we noticed we're missing some detail for our multiple kafka instrumentations

The specification states that peer.service SHOULD be set for kafka producers.

https://github.com/open-telemetry/opentelemetry-specification/blob/a1a8676a43dce6a4e447f65518aef8e98784306c/specification/trace/semantic_conventions/messaging.md#apache-kafka

For Apache Kafka producers, peer.service SHOULD be set to the name of the broker or service the message will be sent to. The service.name of a Consumer's Resource SHOULD match the peer.service of the Producer, when the message is directly passed to another service. If an intermediary broker is present, service.name and peer.service will not be the same.

This should get added across instrumentation's in 1 go

[fbogsany]

There was some discussion here about the difficulty of figuring out which broker a message will go to in ruby_kafka.

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