Add test notification tool (#28334)

* Add test notification tool

* Add frontend styles

* Remove option from admin view

* Refactor create post and add translations

* Fix several CI errors

* Fix API and frontend snapshots

* Refactor trailing and leading icon on buttons

* Add different button states

* i18n-extract

* Fix wrong text

* Add tests

* Fix wrong string

* Fix test

* feat: E2E send test notifications (#28371)

* Refactor send desktop notification

* Address rest of the feedback

* Fix tests

* Add correct link

* Fix test

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Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: yasserfaraazkhan <attitude3cena.yf@gmail.com>

server/i18n/en.json

@@ -5938,6 +5938,26 @@
     "id": "app.notification.subject.notification.full",
     "translation": "[{{ .SiteName }}] Notification in {{ .TeamName}} on {{.Month}} {{.Day}}, {{.Year}}"
   },
+  {
+    "id": "app.notifications.send_test_message.errors.create_post",
+    "translation": "The post cannot be created"
+  },
+  {
+    "id": "app.notifications.send_test_message.errors.no_bot",
+    "translation": "Cannot get the system bot"
+  },
+  {
+    "id": "app.notifications.send_test_message.errors.no_channel",
+    "translation": "Cannot get the system bot direct message"
+  },
+  {
+    "id": "app.notifications.send_test_message.errors.no_user",
+    "translation": "Cannot get the user"
+  },
+  {
+    "id": "app.notifications.send_test_message.message_body",
+    "translation": "If you received this test notification, it worked!"
+  },
   {
     "id": "app.notify_admin.save.app_error",
     "translation": "Unable to save notify data."