PLT-7130 adding more generic push notificaiton message. (#7044)

* PLT-7130 adding more generic push notificaiton message.

* Fixing strings

i18n/en.json

@@ -1811,6 +1811,10 @@
     "id": "api.post.send_notifications_and_forget.push_mention",
     "translation": " mentioned you in "
   },
+  {
+    "id": "api.post.send_notifications_and_forget.push_mention_no_channel",
+    "translation": " mentioned you"
+  },
   {
     "id": "api.post.send_notifications_and_forget.push_message",
     "translation": " sent you a direct message"
@@ -1819,6 +1823,10 @@
     "id": "api.post.send_notifications_and_forget.push_non_mention",
     "translation": " posted in "
   },
+  {
+    "id": "api.post.send_notifications_and_forget.push_non_mention_no_channel",
+    "translation": " posted a message"
+  },
   {
     "id": "api.post.send_notifications_and_forget.push_notification.error",
     "translation": "Failed to send push device_id={{.DeviceId}}, err={{.Error}}"