class_docstr: A basic RL graph manager creates the common scheme of RL where there is a single agent which interacts with a
  single environment.
code: def get_signal_value(self, signal_name):
      return (
          self.level_managers[0]
          .agents["agent"]
          .agent_logger.get_signal_value(signal_name)
      )
  
file_path: coach/rl_coach/graph_managers/basic_rl_graph_manager.py
imports: from typing import Tuple, List
  from rl_coach.base_parameters import AgentParameters, VisualizationParameters, TaskParameters, PresetValidationParameters
  from rl_coach.environments.environment import EnvironmentParameters, Environment
  from rl_coach.filters.filter import NoInputFilter, NoOutputFilter
  from rl_coach.graph_managers.graph_manager import GraphManager, ScheduleParameters
  from rl_coach.level_manager import LevelManager
  from rl_coach.utils import short_dynamic_import
label_desc: Use image node_id 4 for calling the BasicRLGraphManager obj's underlying member method code with example usage: obj.get_signal_value(signal_name) and returns: self