Parse a JSON

Take a string from the value store, and try to parse it as a JSON. If it succeeds, the resulting JSON will be stored in the value store.

Additional inputs

• getGroup: name of the origin key in the sub-store
• getKey: name of the origin sub-store
• resGroup: name of the target sub-store
• resKey: name the value is to be stored as

Function exits

• On success: The string could be parsed and stored properly
• On fail: The string could not be interpreted as a JSON