Convert the onion service authentication panel into an actual prompt
On #41856 (comment 2915738) @pierov commented:
Forcing that kind of panel for the authentication doesn't seem correct to me. Other similar panels are the identity panel, the circuit display, the bookmarks, and, on Firefox, the tracking protection.
They are made to self-close when one changes window. Also, they don't grab user's attention enough, because they're missing fore example an overlay.
I think we should do an actual prompt, like the one for HTTP basic authentication (check for example https://review.torproject.net/).
/cc @donuts