[MM-10458] Change system response to "Could not find the channel" - bug fix (#8738)

* [MM-10458] Change system response to "Could not find the channel" when trying to invite user to private channel you can't see

* add another check to check if user have permission to add another in pvt channel

i18n/en.json

@@ -822,6 +822,10 @@
     "id": "api.command_invite.permission.app_error",
     "translation": "You don't have enough permissions to add {{.User}} in {{.Channel}}."
   },
+  {
+    "id": "api.command_invite.private_channel.app_error",
+    "translation": "Could not find the channel {{.Channel}}. Please use the channel handle to identify channels."
+  },
   {
     "id": "api.command_invite.success",
     "translation": "{{.User}} added to {{.Channel}} channel."