UBERF-7513: Improve notifications model to allow external notifications channels (#6037)

Signed-off-by: Kristina Fefelova <kristin.fefelova@gmail.com>

plugins/gmail/src/index.ts

@@ -15,7 +15,7 @@
 
 import { ChannelItem } from '@hcengineering/contact'
 import type { Account, AttachedDoc, Class, Doc, Ref, Timestamp } from '@hcengineering/core'
-import { NotificationType } from '@hcengineering/notification'
+import { NotificationProvider, NotificationType } from '@hcengineering/notification'
 import type { IntlString, Plugin } from '@hcengineering/platform'
 import { Metadata, plugin } from '@hcengineering/platform'
 import type { Handler, IntegrationType } from '@hcengineering/setting'
@@ -89,7 +89,8 @@ export default plugin(gmailId, {
   },
   string: {
     From: '' as IntlString,
-    To: '' as IntlString
+    To: '' as IntlString,
+    EmailNotificationsDescription: '' as IntlString
   },
   integrationType: {
     Gmail: '' as Ref<IntegrationType>
@@ -108,5 +109,8 @@ export default plugin(gmailId, {
   },
   metadata: {
     GmailURL: '' as Metadata<string>
+  },
+  providers: {
+    EmailNotificationProvider: '' as Ref<NotificationProvider>
   }
 })