[DOCS] Document Avro schemas using "type": "bytes" cannot be automatically deserialized to their logicalType

[lucabelluccini]

When using Avro schema, and the schema contains a field of type bytes with a logicalType (e.g. decimal), the Kafka client is not able to deserialize the field to a correct type, leading to a binary blob encoded string, negating the ability to recover the value as bytes.
We should recommend using native types.