lib: json: add helper macro for array of array

The new JSON_OBJ_DESCR_ARRAY_ARRAY allows use of an array of
array. The macro is based on the comments and directions provided by
Leandro Pereira <leandro.pereira@intel.com> (in #8567).

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Christian Tavares <christian.tavares@ossystems.com.br>