Added imageLink field

Added a new imageLink field to the scenario serialization function which will accompany all elements of the randomizer config.

com.unity.perception/Runtime/Randomization/Scenarios/Serialization/SerializationStructures.cs

     {
         public string name = string.Empty;
         public string description = string.Empty;
+        public string imageLink = string.Empty;
     }
 
     class Group