Add configurable buttons into `st.chat_input`

[lukasmasuch]

Checklist

• [x] I have searched the existing issues for similar feature requests.
• [x] I added a descriptive title and summary to this issue.

Summary

Add support for configurable toggle buttons which are integrated into the chat input field similar to how its supported in many of the LLM-based apps:

Why?

Allows implementing more complex LLM-based apps in Streamlit.

How?

prompt = st.chat_input(..., options=[":material/search: Search", ":material/science: Deep research"])

st.write("Prompt text", prompt.text)
st.write("Selected options", prompt.options)

Additional Context

No response

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