Fixes https://github.com/spring-projects/spring-integration/issues/3686
* Add `src/idea` with respective editor config for IntelliJ IDEA.
Must be imported into an IDE
* Add `src/eclipse` with respective editor config for Eclipse/STS
* Reformat imports in source code according a new editor config
* Migrate Cassandra extension project
* Add `spring-integration-cassandra` module based on the extension project
* Add Java DSL for Cassandra module
* Add documentation
* Add `CassandraContainerTest` based on a Testcontainers
* Fix language in docs
Co-authored-by: Gary Russell <grussell@vmware.com>
* * Fix `reactive-streams.adoc` for a proper link to
the new `spring-integration-cassandra` module
Co-authored-by: Gary Russell <grussell@vmware.com>