fix(emqx_conf_app): print init_load failure to standard_error

logger may not get the chance to spit out the logs before the vm
dies, no matter how long sleep is added before init:stop(1)

apps/emqx_conf/src/emqx_conf_app.erl

@@ -32,12 +32,8 @@ start(_StartType, _StartArgs) ->
         ok = init_conf()
     catch
         C:E:St ->
-            ?SLOG(critical, #{
-                msg => failed_to_init_config,
-                exception => C,
-                reason => E,
-                stacktrace => St
-            }),
+            %% logger is not quite ready.
+            io:format(standard_error, "Failed to load config~n~p~n~p~n~p~n", [C, E, St]),
             init:stop(1)
     end,
     ok = emqx_config_logger:refresh_config(),