NAT support

[supun-io]

• management:init should only add new IP addresses (automatic removal should be disabled)
• ability to manually add an IP address to a server
• each IP address should save a field to save its private IP in a NAT
• Update go sending to use the private IP if available (if no private ip is set, send directly via the public one assuming we can bind to it directly)
• Health check to make sure all private IP routes via the correct public IP (can call OpenDNS or something to get an IP)
• Documentation
• Set up DX to easily test this locally

Notes

• Only NAT 1:1 routing will be supported

[RichMercer]

Is this feature planned? I can't run this on the edge so need to 1:1 NAT this.

[supun-io]

yes, this is planned for the next release

[supun-io]

Notes for a different plan:

- [ ] Support PRIVATE_NETWORK env, which takes CIRD ranges (`10.0.0.0/8` or multiple comma separated)
- [ ] Optionally, users can set NAT_MAP env (`10.0.1.5:203.0.113.10, 10.0.1.6:203.0.113.11`)
- [ ] management:init searches for IPs in this range and checks for public IP reachability