Sample for integrating Core API with chainlit (#6422)

## Why are these changes needed?

This pull request adds new samples that integrates the Autogen Core API
with Chainlit. It closely follows the structure of the
Agentchat+Chainlit sample and provides examples for using a single agent
and multiple agents in a groupchat.
## Related issue number


Closes: #5345

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Co-authored-by: Eric Zhu <ekzhu@users.noreply.github.com>