fix: set parent_id and scope required when listing variables

src/resources/variable/Variable.yaml

@@ -5,12 +5,14 @@ get:
   parameters:
     - in: query
       name: parent_id
+      required: true
       schema:
         type: string
         format: uuid
       description: it filters the list by returning only the variables accessible by the selected parent_id. This field shall contain the id of a project, environment or service depending on the selected scope. Example, if scope = APPLICATION and parent_id=<application_id>, the result will contain any variable accessible by the application. The result will contain also any variable declared at an higher scope.
     - in: query
       name: scope
+      required: true
       schema:
         $ref: '../../schemas/enums/APIVariableScope.yaml'
       description: the type of the parent_id (application, project, environment etc..).