KIP-449 — Add connector contexts to log messages in Connect workers

Accepted Kafka 2.3 Connect

Adds structured logging context (connector name, task ID) to Connect worker log messages using MDC (Mapped Diagnostic Context), so that log entries from different connectors and tasks running in the same JVM can be attributed to their source. Connect worker logs intermix output from multiple threads handling different connectors and tasks, making it extremely difficult to trace a connector failure through log lines without manual correlation.

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