fn parse_config(
        &self,
        _config: &str,
    ) -> Result<Option<LbConfig>, Box<dyn Error + Send + Sync>> {
        Ok(None)
    }
Parses the JSON LB policy configuration into an internal representation.

LB policies do not need to accept a configuration, in which case the
default implementation returns Ok(None).
grpc/src/client/load_balancing/mod.rs