Switch to 4 L2 guards

[mikeperry-tor]

In https://github.com/asn-d6/vanguard_simulator/wiki/Optimizing-vanguard-topologies, we were on the fence between 2-3-8 and 2-4-8 topologies.

In https://gitlab.torproject.org/tpo/core/tor/-/issues/40363, we are heading towards 4 for improved reliability. Plus idk powers of two are nice, and there are more relays now anyway, so sybil risk as a fraction of total has decreased.

If we settle on 4 there, the addon should also use 4. Especially if we only do vanguards-lite there to keep paths short, thus still requiring the addon for high-security cases, for now.

[mikeperry-tor]

This is implemented and is in the changelog.

[mikeperry-tor]

Hrmm, we missed a mention of 2-3-8 in the docs, as per https://gitlab.torproject.org/tpo/core/tor/-/issues/40403#note_2737864

We should also link to vanguards-lite tor ticket in the docs.