Schema Validation with Confluent Platform 5.4

Introduces Schema Validation on write for Confluent Platform 5.4. This feature allows Kafka brokers to validate that data produced to a topic adheres to a registered schema in Confluent Schema Registry. It requires configuring `confluent.schema.registry.url` at the broker level and can be enabled per topic using `confluent.key.schema.validation` and `confluent.value.schema.validation`. The producer protocol is updated to provide specific error feedback for invalid messages within a batch.