Add the new hook agent_fast_reply in process diagram

[sambarza]

The new hook is called here:

 def execute_agent(self, working_memory):
        """Instantiate the Agent with tools.

        The method formats the main prompt and gather the allowed tools. It also instantiates a conversational Agent
        from Langchain.

        Returns
        -------
        agent_executor : AgentExecutor
            Instance of the Agent provided with a set of tools.
        """
        mad_hatter = self.cat.mad_hatter

        # prepare input to be passed to the agent.
        #   Info will be extracted from working memory
        agent_input = self.format_agent_input(working_memory)
        agent_input = mad_hatter.execute_hook("before_agent_starts", agent_input)
        # should we ran the default agent?
        fast_reply = {}
        fast_reply = mad_hatter.execute_hook("agent_fast_reply", fast_reply)            <---------------------
        if len(fast_reply.keys()) > 0:
            return fast_reply
        prompt_prefix = mad_hatter.execute_hook("agent_prompt_prefix", prompts.MAIN_PROMPT_PREFIX)
        prompt_suffix = mad_hatter.execute_hook("agent_prompt_suffix", prompts.MAIN_PROMPT_SUFFIX)