Decorate user-provided instances of ProducerRecord, instead of using them as a raw values

[guillermocalvo]

While looking into #52, I realized Kafka producers can't handle ProducerRecord objects properly at the moment.

Since consumers can receive ConsumerRecord objects, I thought producers should be able to send ProducerRecord objects for the sake of symmetry.

This implementation works for both modes batch/single. Fields not populated by the user may be populated by the context as usual.

@KafkaClient
interface SingleProducer {
    @Topic("foo")
    String sendRecord(ProducerRecord<String, String> record);
}

@KafkaClient(batch = true)
interface BatchProducer {
    @Topic("foo")
    String sendRecords(List<ProducerRecord<String, String>> records);
}

[sdelamo]

@guillermocalvo can you check CI failure?

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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100.0% Coverage
0.0% Duplication

[guillermocalvo]

@guillermocalvo can you check CI failure?

@sdelamo Done 4c6ead5 (it was checkstyle)