Add IPv6 support

[nightah]

This is the first part in a set of changes to add IPv6 support.

Tasks Remaining:

• Add IPv6 support to lancachenet/docker-compose
• Update docs

[nightah]

@GotenXiao, @Crabbey and @VibroAxe I know we briefly spoke about this on Discord, it's probably worthwhile unifying this along with the other IPv6 PR's where relevant.

Should I rebase this and change the ENABLE_IPV6 switch to be called ENABLE_V6 like lancachenet/lancache-dns#112, or should we have @Crabbey change the aforementioned PR?

Just looking for direction so the changes I'm making both to the docs and lancachenet/docker-compose can be introduced seamlessly by way of merging the relevant PR's.

[stale]

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[VibroAxe]

Oops, forgot to flag this as an enhancement
We need a strategy about ipv6 @MathewBurnett and I were talking about this the other day.

The main issue is that ipv6 isn't the issue, it's the fact that the various tunnelling configs setup by the user tend to result in things missing the cache. Not really sure how we get round that until v6 in the house becomes more functional

[VibroAxe]

We're also planning a large refactor to make generic depend on monolithic, not the other way round which will probably require some extensive modifications to this PR/moving it into monolithic