Add Dataflow Example on streaming analytic to handle schema changes

[ihaffa-google]

Using schema enforcement and DLT (Dead Letter Table) approach to handle schema changes when reading and inserting data to BQ. Code include example and unit tests

[iht]

The build is failing with this error:

Some files need to be formatted in ./examples/dataflow-streaming-schema-handler - FAIL
./examples/dataflow-streaming-schema-handler/src/main/java/com/google/cloud/pso/pipeline/PubsubToBigQueryJSON.java
./examples/dataflow-streaming-schema-handler/src/main/java/com/google/cloud/pso/util/BigQueryConverters.java