Add human-in-the-loop capabilities

[tituslhy]

Is your feature request related to a problem? Please describe. There are more agentic applications that have human-in-the-loop as a feature (implemented in langgraph, llamaindex, and autogen). There is currently no feature in chainlit that supports this natively.

Describe the solution you'd like It would be great if chainlit has abstractions that support users in developing human-in-the-loop agentic apps!

Additional context Here are some examples of human-in-the-loop applications from the official docs of the respective libraries. langgraph: https://langchain-ai.github.io/langgraph/how-tos/human_in_the_loop/wait-user-input/ llamaindex: https://colab.research.google.com/github/run-llama/llama_index/blob/main/docs/docs/examples/agent/agent_runner/agent_runner_rag_controllable.ipynb autogen: https://microsoft.github.io/autogen/docs/tutorial/human-in-the-loop/