fix(exhook): fix the error message of unknown hookpoint

Now if there is an unknown hookpoint, the error message is actually `{unknown_hookpoint,{error,badarg}}`,
the hookpoint name information is lost

apps/emqx_exhook/src/emqx_exhook_server.erl

@@ -231,7 +231,7 @@ resolve_hookspec(HookSpecs) when is_list(HookSpecs) ->
                         end,
                     case {lists:member(Name, AvailableHooks), lists:member(Name, MessageHooks)} of
                         {false, _} ->
-                            error({unknown_hookpoint, Name});
+                            error({unknown_hookpoint, Name0});
                         {true, false} ->
                             Acc#{Name => #{}};
                         {true, true} ->