Temporarily disabling JSON OPL/ITL validation

cc: @benoit.seignovert

Considering that JUICE SOC frequently delivers JSON OPL/ITL files that not compliant to their own schemas, I'm proposing to modify the readers so that the validation is disabled by default; this until the SOC has stabilised their JSON OPL/ITL schemas. For example using an optional validate argument for the read_itl_json(), read_opl_json() and read_opl() functions.

Edited by Nicolas Manaud