add cleanup websocket messages button

[ceifa]

A clear messages button, like browsers network inspect have

[pimterry]

Thanks! I did a little clearup here (the requirement to use .downstream should have been a type error, but wasn't - the 'view' upstream/downstream thing for WebSockets is new and isn't really widely used yet) so I've fixed that first, and I've tweaked the delete icon to match the rest, but otherwise all looks good I think! 👍

[ceifa]

I was a little bit confused about how the types are structured, thank you for fixing it! The idea of the icon is that it matches the icon chromium uses for the same feature, but the one you used is good too!