Arti: enforce our stream isolation design

Current design: https://tails.net/contribute/design/stream_isolation/

See the separate SocksPorts and their isolation flags in config/chroot_local-includes/etc/tor/torrc. We want the same stream isolation configuration for arti.

First of all we need to figure out if arti changes the stream isolation defaults, and if/when they will support the various flags, or if this whole topic will be substantially different so we need to revisit Tails' design.