fix(chat): Force a scroll-bar if we have messages

What does this MR do?

refactor(DuoChat): Simplify Duo Chat history markup

This moves the global scrollbar to be local only for the history tab. The different levels of the DOM also have been reduced and some animations being simplified a little bit.

fix(DuoChat): Force a scroll-bar if we have messages

This will allow us to make sure that the "scrolling-to-bottom" works properly, as overflow-anchor needs an overflow to work at all.

Screenshots or screen recordings

Note	Before	After
As soon as we have a message, the history is always scrollable
After this change the scrollbar just extends alongside the history, rather than the whole page
After this change, the chat sticks to the bottom in case the first message pushes the history to be taller	Screen_Recording_2024-02-19_at_23.14.21	Screen_Recording_2024-02-19_at_23.12.32

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