KAFKA-13881: Add Streams package infos

[gharris1727]

Signed-off-by: Greg Harris greg.harris@aiven.io

Split off from #12895 to target only Streams packages.

There are currently no descriptions of packages in the javadocs, which can be intimidating to new users that look at the documentation and see a wall of raw package names. An example of this can be seen here: https://kafka.apache.org/31/javadoc/

This change adds the following package descriptions based on a best-effort reading of the existing javadocs. Please feel free to correct any factual errors in the proposed descriptions, I am not asserting that these descriptions are currently accurate. This PR only covers the streams packages.

For clarity of review, I'll summarize the new descriptions in a table. This summary may become stale by accident, so please be sure to view the diff itself or build the changes locally with ./gradlew javadoc.

Package	Description
org.apache.kafka.streams	Provides the Kafka Streams library for building streaming data applications.
org.apache.kafka.streams.errors	Provides common exception classes for Streams applications.
org.apache.kafka.streams.kstream	Provides a high-level programming model (DSL) to express a (stateful) data flow computation over input streams and tables.
org.apache.kafka.streams.processor	Provides a low-level programming model (Processor API, aka, PAPI) to express a (stateful) data flow computation over input topics.
org.apache.kafka.streams.processor.api	Provides a low-level programming model (Processor API, aka, PAPI) to express a (stateful) data flow computation over input topics.
org.apache.kafka.streams.query	Provides a query API (aka Interactive Queries) over state stores, for extracting data from a stateful Kafka Streams application.
org.apache.kafka.streams.state	Provides interfaces for managing the intermediate state of a stateful streams application.
org.apache.kafka.streams.test	Provides classes for testing Kafka Streams applications with mocked inputs.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[mimaison]

@mjsax @ableegoldman Can you take a look? Thanks

[mjsax]

Thanks for the PR, @gharris1727.

Merged to trunk and cherry-picked to 3.4 branch.