Enable configuration of Java transforms (specifically IO) through other SDKs

Since https://github.com/apache/beam/pull/7316 we can reference external transforms which are transforms only available in a "foreign" SDKs. This allows us to fill the gap in terms of missing transforms in the Python and Go SDK, specifically IO transforms.

We can start collecting/exposing transforms that Beam users need. The following transforms could be interesting:

• KafkaIO / KinesisIO
• CassandraIO / ElasticserchIO / Hbase / Redis
• JDBC
• S3 file system
• GenerateSequence

See also https://s.apache.org/beam-cross-language-io and BEAM-6485.

CC robertwb chamikara thw