Add workflow validator for attachments during transition

Problem Statement : 

Validating Attachment during Transition. 

Summary :

Need to be able use Validator to verify if any attachment is added to ticket. If yes only then transition should happen. If not it should throw an exception. 

At the moment, per the current design, no matter attachment is added or not, transition will always throw an error. It works as expected if we add a screen during transition with Attachment field. it will be successful if user attach an attachment (on screen during transition) else it will fail. 

Conclusively validator configured for attachment does not validate pre-existing attachments and works only when during transition we add a screen and then attach files. 

Requirement: 

Validator for attachment should also work like all other fields. It should not be necessary to attach attachment on screen during transition but it should validate pre-existing attachments as well.