docs: update Kafka programming guide

[leto-b]

Summary

• Replace the Kafka programming guide with a concise IoTDB Kafka user manual.
• Keep only the essential Kafka producer/consumer and IoTDB write path snippets.
• Add environment prerequisites, message format, dependency notes, and a query validation example.
• Sync the same content to the zh/en latest and Master variants.
• Link to the complete sample project in iotdb-extras.

Notes

• Kafka installation, startup, and program execution steps are intentionally omitted and delegated to the Kafka official documentation.