[WIP] Support hpo in distributed

[rayrayraykk]

I add a function of sending cfg before starting for run HPO in distributed mode. But it's not enough to change self._cfg when the client receives a new configuration because some instances are created based on old cfg, and we need to add a reset method for the worker to achieve this, just as the trainer does, see https://github.com/alibaba/FederatedScope/blob/b5870f733af5cac2863a4e89742bc967a9cf0a0d/federatedscope/core/trainers/trainer.py#L77

And due to the limitations of gRPC, some vFL model and feature engineering methods can't work properly for the type of message might vary. In order to send such data, we may need a module for type conversion.

@xieyxclack @joneswong