[Refactor] Chat control should scroll down to focus on the last message when a new message appears

[AlexandreSajus]

Description

When a new message appears in the chat control, the chat control should scroll to the last message. This assumes that #1586 is fixed. Use https://demo-llm-chat.taipy.cloud/ as reference: when I receive a new message from GPT, the chat window scrolls down to the message and highlights it:

Acceptance Criteria

• [ ] Ensure new code is unit tested, and check code coverage is at least 90%.
• [ ] Propagate any change on the demos and run all of them to ensure there is no breaking change.
• [ ] Ensure any change is well documented.

Code of Conduct

• [X] I have checked the existing issues.
• [ ] I am willing to work on this issue (optional)