Add a mixed+hs-v23-ipv6 network to chutney

We want to test our new IPv6 code in mixed networks, so let's add a mixed+hs-v23-ipv6 network to chutney.

It should be pretty much a copy-paste from mixed+hs-v23 and hs-v23-ipv6-md.

(There's no need for a non-md variant, all supported tor versions can use microdescriptors for IPv6 onion services.)

Proposed design:

• 2 dual-stack authorities,
• 2 IPv4-only relays,
• 2 dual-stack relays
• 2 IPv6-only v2 onion services
• 2 IPv6-only v3 onion services
• 2 IPv6-only clients For each kind of node, one should be a new version, and one should be an old version.

Other networks test IPv4-only authorities and clients, so we don't need them. (But we want to test IPv4 and dual-stack relays in the same network.)