Maybe enable full-vanguards in arti-client and arti TorProvider implementations

[morganava]

Arti has full vanguards (which required some complicated non-sense for legacy c-tor) built-in. We should optionally enable it

See blog post for details:

• https://blog.torproject.org/announcing-vanguards-for-arti/

[morganava]

See also: https://spec.torproject.org/vanguards-spec/vanguards-lite.html

Perhaps should be configurable with some documentation for the different potential use cases.