Add processed_at field to the order

processed_at gives more relevant information for order's timestamp because created_at can be based on time when the orders are imported to the store

src/main/java/com/storakle/shopify/domain/JsonConstants.java

@@ -14,6 +14,7 @@ public final class JsonConstants
     public static final String FIRST_NAME = "first_name";
     public static final String LAST_NAME = "last_name";
     public static final String CREATED_AT = "created_at";
+    public static final String PROCESSED_AT = "processed_at";
     public static final String ACCEPTS_MARKETING = "accepts_marketing";
     public static final String NOTE = "note";
     public static final String TAGS = "tags";

src/main/java/com/storakle/shopify/domain/Order.java

@@ -45,4 +45,9 @@ public class Order
     @JsonDeserialize(using = FlexDateDeserializer.class)
     @JsonSerialize(using = FlexDateSerializer.class)
     private Date createdAt;
+
+    @JsonProperty(value = JsonConstants.PROCESSED_AT)
+    @JsonDeserialize(using = FlexDateDeserializer.class)
+    @JsonSerialize(using = FlexDateSerializer.class)
+    private Date processedAt;
 }