Kafka API constraints

YDB supports Apache Kafka protocol version 3.4.0 with the following constraints:

1. Only authenticated connections are allowed.
2. Only SASL/PLAIN authentication method is supported.
3. Message compression is not supported.
4. Transactions are not supported.
5. DDL operations are not supported. Use the YDB SDK or YDB CLI to perform them.
6. Data schema validation not supported.
7. Kafka Connect is only supported in standalone mode.