WIP: Add NAT support through the use of /advertise(Addr|Port)/

[stevefan1999-personal]

Fixes #8

This could benefit some hypothetical cloud-to-cloud situation that had to be communicated though internet, e.g. interconnect from AWS to GCP without using their overpriced VPN service.

By default the advertise address would be ~the same as the final bind address~anything you want if and only if it is a valid IP address otherwise empty to keep track with the default in memberlist, and advertise port is not yet changeable (implied by ClusterPort). The behavior is the same as before if you don't use the advertise address.

This is not yet finished due to missing tests

[agrrh]

Just to let you know, I've faced exact cloud-to-cloud situation, would be really glad to see this finished and merged in :+1:

[pri11er]

This enhancement is working perfectly with AWS, OCI and other clouds. Thank you for the effort. Hopefully this project will become active again someday.

[t0xicCode]

@stevefan1999-personal do you need/want assistance with this?

[stevefan1999-personal]

@t0xicCode Sure, I have been busy about real life work and could hardly take time to finish some of the PRs myself.