add a run time agent master to schedule current active users for training
Created by: guru4elephant
we need to add an agent master node during training:
- there can be thousands of users who participate FL training, and in each FL step, only hundreds of users can do training. a scheduler should assign current active users that can do training
- Different scheduling algorithms can be implemented in the run-time agent master
- for industrial deployment, an agent master is easier to collect information of all workers and servers.