Add OTel GenAI traces:
- `create_agent`
- `invoke_agnet`
- `execute_tool`
Introduces context manager helpers to create these traces. The helpers
also serve as instrumentation points for other instrumentation
libraries.
Resolves#6644
## 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>