feat(core): Add field parent_ticket to base ticket view serializer

ref: #517 #522

app/core/serializers/ticket.py

@@ -143,6 +143,7 @@ class TicketModelSerializer(
             'modified',
             'status',
             'status_badge',
+            'parent_ticket',
             'title',
             'description',
             'estimate',
@@ -324,6 +325,8 @@ class TicketViewSerializer(TicketModelSerializer):
 
     category = TicketCategoryBaseSerializer()
 
+    parent_ticket = TicketBaseSerializer()
+
     opened_by = UserBaseSerializer()
 
     organization = OrganizationBaseSerializer(many=False, read_only=True)