MAINTAINERS: Added myself as JSON collaborator
MAINTAINERS: Added myself as JSON collaborator

Added myself as collaborator for the JSON library, added files json.c/.h

Signed-off-by: Ramiro Merello <44d6dec2a3225ed89c29d123afc99bb50b73da0e@itba.edu.ar>

zephyrproject-rtos/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr