[PLT-5864] Move teammate name display setting to the System Console (#6681)

* move teammate name display setting to the system console

* update all the likes of TeammateNameDisplay names

* fix gofmt error

* rebase and fix conflict

i18n/en.json

@@ -4311,6 +4311,10 @@
     "id": "model.config.is_valid.sql_query_timeout.app_error",
     "translation": "Invalid query timeout for SQL settings.  Must be a positive number."
   },
+  {
+    "id": "model.config.is_valid.teammate_name_display.app_error",
+    "translation": "Invalid teammate display.  Must be 'full_name', 'nickname_full_name' or 'username'"
+  },
   {
     "id": "model.config.is_valid.time_between_user_typing.app_error",
     "translation": "Time between user typing updates should not be set to less than 1000 milliseconds."