add submitter metadata

app/controllers/api/submissions_controller.rb

@@ -132,7 +132,7 @@ module Api
         include: {
           submitters: { only: %i[id slug uuid name email phone
                                  completed_at opened_at sent_at
-                                 created_at updated_at external_id],
+                                 created_at updated_at external_id metadata],
                         methods: %i[status application_key] },
           template: { only: %i[id name created_at updated_at] },
           created_by_user: { only: %i[id email first_name last_name] }
@@ -147,7 +147,7 @@ module Api
           message: %i[subject body],
           submitters: [[:send_email, :send_sms, :completed_redirect_url, :uuid, :name, :email, :role,
                         :completed, :phone, :application_key, :external_id,
-                        { values: {}, readonly_fields: [], message: %i[subject body],
+                        { metadata: {}, values: {}, readonly_fields: [], message: %i[subject body],
                           fields: [%i[name default_value title description
                                       readonly validation_pattern invalid_message]] }]]
         }