Refactor CDC Debezium Source

[tzolov]

• New debezium-source implementation, build on the Debezium Engine API. No forking of Debezium code.
• Based on latest 2.2.0 CR1 Debezium version.
• Supports for MySQL, PostgreSQL, Oracle, SQL Server, MongoDB, DB2, Vitess and Spanner datastores.
• Supports JSON, AVRO and (Experimental) PROTOBUF content formats with byte[] encoding. Defaults to JSON.
• Configuration is split into Debezium Engine auto-config and Consumer change-event configuration. Later allows for plugging different consumer implementation.
  • Default Consumer implementation obeys the functional Supplier contract (e.g. exposes a Supplier<Flux<Message<?>>>).
  • The Debezium Engine Auto-Configuration offers hooks to set the OffsetCommitPolicy, ConnectorCallback, CompletionCallback and Clock. Sensible defaults are implemented.
• Removed MetadataStore as option for commit offset storage.
• Removed the spring property shortcuts. Only the native Debezium properties are supported. Use the debezium.properties.* prefix for set any native property.
• Removed the old Debezium suppler&source code. Rename the source to debezium-source.

[corneil]

• Add support for DB2, Cassandra, Vitess, Spanner
• Add AVRO format support. Defaults to JSON
• Remove the Metadata repo configuration.
• Remove the Spring property sortcuts. Only the native Debezium properties are used.
• change the native properties prefix from cdc.config to cdc.debezium.
• Removes the need to fork and modify the Debezium engine code.
• Add binding name strategy.
• Update to latest 2.1.4 Final version.

This is a new Debezium source implementation, build on the Debezium Engine API. I've removed the support for metadata registry as it requires forking and modifying Debezium code. Above changes also means that the new implementation is not backward compatible. This is the reason to add new cdc-debezium-sourc2 and cdc-debezium-spupplier2 instead of modifying the original.

The current implementation is a source and does not implement the contract of functional Supplier. Many of the source implementations provides Spring Integration MessageProducer which is then used to create Supplier<Flux<Message<?>>>

[tzolov]

@corneil the code and description are updated. The implementation does implement the Supplier contract and exposes Supplier<Flux<Message<?>>>.

[tzolov]

Addressed all open review recommendations, including a StepVerifier test for the Supplier<Flux<Message<?>>> debeziumSupplier and updated mongodb testing, though later still require manual testing (description provided in the README).

[artembilan]

Merged as https://github.com/spring-cloud/stream-applications/commit/6cf66ec779faaed28a759dde409b034c92cb7356 after rebasing.

@tzolov , huge thanks: as always tremendous work!

Looking forward for more! 😄