MM-20347 Move ID Loaded Push Notifications to E20 (#13185)

* Move ID Loaded Push Notifications to E20

* Fix model tests

einterfaces/notification.go

@@ -0,0 +1,13 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package einterfaces
+
+import (
+	"github.com/mattermost/mattermost-server/model"
+)
+
+type NotificationInterface interface {
+	GetNotificationMessage(ack *model.PushNotificationAck, userId string) (*model.PushNotification, *model.AppError)
+	CheckLicense() *model.AppError
+}