[feat][io] Add Debezium Db2 source connector

[david-streamlio]

Motivation

Debezium ships a Db2 source connector (io.debezium:debezium-connector-db2, present in the debezium-bom at our pinned version), but this repository does not wrap it. We currently wrap 5 of Debezium's 12 source connectors: MySQL, PostgreSQL, MongoDB, Oracle, and SQL Server.

Db2 is a mature Debezium connector with real enterprise demand, and its CDC model (capture tables, populated by an ASN capture agent) is close enough to SQL Server's that the existing debezium/mssql module is a reasonable structural template.

Proposal

Add a debezium/db2 module (pulsar-io-debezium-db2) following the structure of the existing Debezium modules:

• DebeziumDb2Source extending DebeziumSource
• include("debezium:pulsar-io-debezium-db2") in settings.gradle.kts
• debezium-connector-db2 = { module = "io.debezium:debezium-connector-db2" } in the version catalog
• NAR packaging + distribution wiring
• A Testcontainers integration test using the icr.io/db2_community/db2 image

Notes

• Check whether Db2 is a multi-partition connector. If it is, it will hit the same task.id gap as SQL Server ([Bug] Debezium SQL Server source fails to start: multi-partition connector never receives task.id #61), where AbstractKafkaConnectSource never calls connector.taskConfigs() for Debezium sources. [Bug] Debezium SQL Server source fails to start: multi-partition connector never receives task.id #61 should ideally land first.
• Verify the Db2 JDBC driver (com.ibm.db2:jcc) reaches the NAR at runtime; debezium-connector-db2 may not bundle it. (For comparison, debezium-connector-oracle does pull ojdbc11 transitively — verified in [improve][test] Add Debezium Oracle source integration test #62.)
• The Db2 container image is large and requires accepting a license and privileged mode; evaluate CI runtime cost before committing to running its test on every PR.
• Use the GenericContainer pattern (see the Testcontainers version conflict noted in [improve][test] Add Debezium Oracle source integration test #62).

Identified by a scan of the Debezium connector catalog against our connector inventory.