Provide DoFn to convert a Row (record with schema) to a javax.json.JsonObject

This task is about ensuring the generic record of beam can be converted to a more mainstream format (JSON). The usage os javax.json.JsonObject is to ensure it is portable and implementation independent and integrates th emost probably with client libraries (most implementations have a bridge to the jsr anyway)

It will likely lead to provide a Dofn Row -\> JsonObject and the opposite.

Imported from Jira [BEAM-4381](https://issues.apache.org/jira/browse/BEAM-4381). Original Jira may contain additional context.
Reported by: romain.manni-bucau.