Use TextAreaInput with auto_grow as default for ChatInterface

[ahuang11]

Right now, it's not possible to enter new lines in the default ChatInterface without setting widgets=[pn.widgets.TextAreaInput(auto_grow=True)]

However, the downside of using TextAreaInput is that the message doesn't get sent on pressing "enter" which can be tedious.

[MarcSkovMadsen]

I think we should implement a real ChatInput that works exactly like ChatGPT's input. And then change.

It's great if the ChatInput optionally provides the undo, clear etc buttons.