Added createdAtVersion property to newly created notifications

refs https://linear.app/tryghost/issue/CORE-64/resolve-undissmissable-update-notification-banners

- The property is meant to track Ghost instance version the notification was received and processed at.
- This information should be useful in the future to dismiss outdated notifications

core/server/api/canary/utils/serializers/output/notifications.js

@@ -19,6 +19,7 @@ module.exports = {
             delete notification.seen;
             delete notification.seenBy;
             delete notification.addedAt;
+            delete notification.createdAtVersion;
         });
 
         frame.response = {

core/server/api/v2/utils/serializers/output/notifications.js

@@ -19,6 +19,7 @@ module.exports = {
             delete notification.seen;
             delete notification.seenBy;
             delete notification.addedAt;
+            delete notification.createdAtVersion;
         });
 
         frame.response = {

core/server/api/v3/utils/serializers/output/notifications.js

@@ -19,6 +19,7 @@ module.exports = {
             delete notification.seen;
             delete notification.seenBy;
             delete notification.addedAt;
+            delete notification.createdAtVersion;
         });
 
         frame.response = {

core/server/services/notifications/notifications.js

@@ -123,7 +123,8 @@ class Notifications {
             dismissible: true,
             location: 'bottom',
             status: 'alert',
-            id: ObjectId().toHexString()
+            id: ObjectId().toHexString(),
+            createdAtVersion: this.ghostVersion.full
         };
 
         const overrides = {

test/unit/server/services/notifications/notifications.test.js

@@ -194,6 +194,7 @@ describe('Notifications Service', function () {
             createdNotification.dismissible.should.be.false();
             createdNotification.top.should.be.true();
             createdNotification.message.should.equal('Hello test world!');
+            createdNotification.createdAtVersion.should.equal('4.1.0');
         });
     });