Define return user message from controller or context

Currently when you wish return a message to a user after an event request, you need to set it ine the called event.

for a service in java :

  ServiceUtil.returnSuccess("Your service is a success")

for a service in groovy :

  return success("Your service is a success")

for a Java class :

 request.setAttribute("_EVENT_MESSAGE_", "Your service is a success");

If during an integration, you want to use standard service like createProduct, createPartyRelationship, and need a specific message for users, you need to define you own service.

For escape this case and increase the service reusability, I propose to implement a new systeme to override the event return by a definition depending the buisness context.

For that two improvement :
1. Add new child element to reques-map->response on the controller

• With given the exact value

       <response name="success" type="request" value="json">
           <return-user-message value="Your service is a success"/>
       </response>

• With a flexible expander

      <response name="success" type="request" value="json">
         <return-user-message value="Your service to change is a success"/>
      </response>
      

• With a property

      <response name="success" type="request" value="json">
         <return-user-message ressource="CommonUiLabels" value="CommonSuccessfullyCreated"/>
      </response>
      

• From a context field

      <response name="success" type="request" value="json">
         <return-user-message from-field="mySpecificReturnMessage"/>
      </response>
      

2. From the context directly sent from the form 

 <form name="CallEvent" target="MyEvent" .. >
     <field name="_CUSTOM_EVENT_MESSAGE_"> <hidden value="Your service to change is a success"/>
     <field name="_CUSTOM_ERROR_MESSAGE_"> <hidden value="Your service failed"/>

related thread on dev : https://lists.apache.org/thread/bv46xndbny6phfxycbmbmxs4t2n7jr28