feat: add ipv6 support

[NoobTW]

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Lack of IPv6 Auto Assignment support.

Issue Number: #6 #89

What is the new behavior?

What's working (These are tested on another ZT client.):

• Add checkbox to auto-assign ZeroTier RFC4193 IP
• Add checkbox to auto-assign ZeroTier 6PLANE IP
• Add hints about what RFC4193/6PLANE IPs would look like (the yellow part is the network addr; the blue part is the client addr.; IPv6 hints ref)

What's not working yet:

• Auto-Assign from a specific Range. Would need to add two more textboxes, and the handleChange might affect IPv4's ipAssignmentPools. Haven't tried it, tho.
• Hint about what 6PLANE IP would look like. I don't know where's the yellow part of 6PLANE ip.
• Show assigned IP on the members page. (I haven't find the assigned IP in the config object yet. might need to take a deeper look at zero-ui backend)

Does this introduce a breaking change?

• Yes
• No

Other information

[dec0dOS]

Thanks for your PR, @NoobTW!

Currently, IPv6 in ZeroTier is still a black box for me, so I could not accept the half-baked feature. If you couldn't finish the IPv6 feature by yourself, please don't delete your PR, as your research would be really helpful in the future.

[NoobTW]

I respect your call, as you're the primary maintainer of this repo.

However, the main function (6PLANE and RFC4193 assignment) is working. The non-working part is just about showing assigned/managed IPs. Personally, I think we can still call it a checkpoint/milestone or something.

But it's not a bad thing to wait and see if the community can help.

Again, it's fine with me if you decide to keep this PR open. (not trying to be rude)

[NoobTW]

This might be helpful to calculate the twp IP addresses.

https://gist.github.com/laduke/fa1e9a68a79d9038ab117ad0ab69927a

[mikkelke]

I really need this to use zero-ui. Can i be any help?

[NoobTW]

Made a few progress.

What's working now:

• Auto assign IPv6s (Both RFC4193 and 6PLANE) with hints (see screenshots above).
  • I've double checked the IPs from clients, looks correct now.

What's not working yet:

• Assign IPv6s from range. (However, as this comment pointed out, I also believe this can be a separate issue.)
• Display assigned IPv6 addresses at the members area.