code: func ConfigSchema() *schema.Schema {
  	return &schema.Schema{
  		Type:        schema.TypeMap,
  		Description: "A list of custom attributes to set on this resource.",
  		Optional:    true,
  	}
  }
docs: // ConfigSchema returns the schema for custom attribute configuration
  // for each resource that needs it.
  //
  // The key should be set to the ConfigKey constant and should be a
  // map of custom attribute ids to values.