Support the IPv6 endpoint.

[adamchainz]

No description provided.

[adamchainz]

Unsure about making this the default. Docs:

The IPv6 address is only accessible on Instances built on the Nitro System.

And:

The following instances are built on the Nitro System:

Virtualized: A1, C5, C5a, C5ad, C5d, C5n, C6g, C6gd, C6gn, C6i, D3, D3en, DL1, G4, G4ad, G5, G5g, I3en, Im4gn, Inf1, Is4gen, M5, M5a, M5ad, M5d, M5dn, M5n, M5zn, M6a, M6g, M6gd, M6i, p3dn.24xlarge, P4, R5, R5a, R5ad, R5b, R5d, R5dn, R5n, R6g, R6gd, R6i, T3, T3a, T4g, high memory (u-*), VT1, X2gd, and z1d

Bare metal: a1.metal, c5.metal, c5d.metal, c5n.metal, c6g.metal, c6gd.metal, i3.metal, i3en.metal, m5.metal, m5d.metal, m5dn.metal, m5n.metal, m5zn.metal, m6g.metal, m6gd.metal, mac1.metal, r5.metal, r5b.metal, r5d.metal, r5dn.metal, r5n.metal, r6g.metal, r6gd.metal, r6i.metal, u-6tb1.metal, u-9tb1.metal, u-12tb1.metal, u-18tb1.metal, u-24tb1.metal, x2gd.metal, and z1d.metal

Well that's not all of them.

Maybe we could try autodetect if IPv6 can be used? Or just make it an option for now, since few instances are IPv6 only?