101 featch available variables from previous steps (#8062)

- add outputSchema in workflow step settings
- use outputSchemas to compute step available variables


https://github.com/user-attachments/assets/6b851d8e-625c-49ff-b29c-074cd86cbfee

packages/twenty-front/src/modules/workflow/utils/getTriggerDefaultDefinition.ts

@@ -26,6 +26,7 @@ export const getTriggerDefaultDefinition = ({
         type,
         settings: {
           eventName: `${activeObjectMetadataItems[0].nameSingular}.${OBJECT_EVENT_TRIGGERS[0].value}`,
+          outputSchema: {},
         },
       };
     }