Description of the new feature/enhancement

The title says it all.
This is another really good thing that Windows Terminal could borrow from felixse/FluentTerminal.
This would basically expand the current terminal's background (including all the modifications done to it, for example a custom background image or opacity level) over to the titlebar (including the minimize, maximize and close icons).
This would make it consistent with other Windows apps following Fluent Design (think of the Settings app and its titlebar), apart from making it look really cool.
Attached here is a screenshot of Fluent Terminal (with acrylic blur and without any background image):

Proposed technical implementation details (optional)

While digging for similar requests (I couldn't find an issue that addressed this specifically), I read somewhere that such a thing isn't possible given the architecture. Well, if that's the case, too bad. But I'm still opening the issue so that this remains documented somewhere separately.