PostgreSQL writer

[mojodna]

Current implemented for streaming sources as a foreachWriter, but would be more general if it were actually a sink.

Sources of inspiration:

• https://github.com/phatak-dev/spark2.0-examples/blob/master/src/main/scala/com/madhukaraphatak/examples/sparktwo/datasourcev2/MysqlWithTransaction.scala
• https://www.slideshare.net/datamantra/understanding-transactional-writes-in-datasource-v2-109643509
• http://blog.madhukaraphatak.com/spark-datasource-v2-part-6/

[mojodna]

Also see https://docs.databricks.com/spark/latest/data-sources/sql-databases.html#write-data-to-jdbc

[mojodna]

If only getInsertStatement could be overridden...