Add option to log lines in JSON

[rgordill]

This feature provides better support for ingesters that processes json to structure the logs, like elasticsearch, loki, etc.

https://www.postgresql.org/docs/current/runtime-config-logging.html#RUNTIME-CONFIG-LOGGING-JSONLOG

[rgordill]

For your records, that would be only available from v15: https://www.postgresql.org/docs/release/15.0/