upgrader: documentation fix

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>
formatter: 'recjson' format addition

* Adds general implementation of 'recjson' using formatter engine.
  (addresses #1908)

* Adds an upgrader recipe for the new output format.

Signed-off-by: Eirini Psallida <eirini.psallida@cern.ch>
Reviewed-by: Jiri Kuncar <jiri.kuncar@cern.ch>