Why Producer not support send messages for batch

**Is your feature request related to a problem? Please describe.**
4.x client support send batch，but 5.x not support，and the producer implement support batch

**Describe the solution you'd like**
Add function List send(List messages) throws ClientException;

Start with the Producer API definition and its existing single-message send operation, then compare the 4.x and 5.x client APIs described in the issue. Done means the 5.x Producer API exposes the requested batch send operation with consistent return and exception types; no file or test location is provided.

Written by the indexing model from the issue text.