docstr: load all users' data into manager
docstr_tok: ["load","all","users","'","data","into","manager"]
code: def load_users(self):
      """
      load all users' data into manager
      """
      self.users = {}
      self.user_record = pd.read_csv(self.users_file, index_col=0)
      for user_id in self.user_record.index:
          self.users[user_id] = self.load_user(user_id)
  
file_path: qlib/qlib/contrib/online/manager.py
imports: import yaml
  import pathlib
  import pandas
  import shutil
  from ...backtest.account import Account
  from .user import User
  from .utils import load_instance, save_instance
  from ...utils import init_instance_by_config
label_desc: Use image node_id 2 for calling the UserManager obj's underlying member method code with example usage: obj.load_users() without return types