[MM-38082] Add local-mode handler for config reload endpoint (#18252)

* Add local-mode handler for config reload endpoint

* Remove redundant method

api4/config_test.go

@@ -126,10 +126,10 @@ func TestReloadConfig(t *testing.T) {
 		CheckForbiddenStatus(t, resp)
 	})
 
-	t.Run("as system admin", func(t *testing.T) {
-		_, err := th.SystemAdminClient.ReloadConfig()
+	th.TestForSystemAdminAndLocal(t, func(t *testing.T, client *model.Client4) {
+		_, err := client.ReloadConfig()
 		require.NoError(t, err)
-	})
+	}, "as system admin and local mode")
 
 	t.Run("as restricted system admin", func(t *testing.T) {
 		th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ExperimentalSettings.RestrictSystemAdmin = true })