use Python decorator to simplify the registration process

[sonichi]

          This design is great, which can help many applications and agents in multi-agent scenarios.

1. Can we use Python decorator to simplify the registration process? (Not a big issue. Just thinking loud).

   class ChildAgent(ResponsiveAgent):
    @register(MathAgent)
    def reponse_for_math_agent(...):
          ...

2. Why use "class_type" as a decision variable. The agent's name can ne another thing to consider (e.g., in the OptiGuide example, where both Writer and Safeguard are ResponsiveAgent).

_Originally posted by @BeibinLi in https://github.com/microsoft/FLAML/pull/1165#discussion_r1282221107_