code: @Nullable
      static PluginGroup loadPlugins(PluginTarget target, CentralDogmaConfig config) {
          return loadPlugins(PluginGroup.class.getClassLoader(), target, config);
      }
docs: Returns a new {@link PluginGroup} which holds the {@link Plugin}s loaded from the classpath.
  {@code null} is returned if there is no {@link Plugin} whose target equals to the specified
  {@code target}.
  
  @param target the {@link PluginTarget} which would be loaded