Tor Browser: Improve TBB UI of hidden service client authorization

This is the parent ticket for Sponsor27 Objective1 Activity1 about improving the UI of client authorization.

This used to be #14389 (moved), but it contained too many network-team-specific information so I repurposed #14389 (moved) to be about the network-team side of things, and please use this ticket for the Tor Browser side of things.

Resources about setting up client auth: https://2019.www.torproject.org/docs/tor-onion-service.html.en#CookieAuthentication https://lists.torproject.org/pipermail/tor-project/2019-January/002180.html and https://github.com/torproject/tor/blob/7741b21d0e3afbfc6d60a852fce6992724c4ae71/doc/tor.1.txt#L3021 and https://github.com/torproject/tor/blob/7741b21d0e3afbfc6d60a852fce6992724c4ae71/doc/tor.1.txt#L1122