feat(nginx): Add support for IPv6

[cogk]

Add IPv6 listen directives to Nginx configuration templates

I believe that agent services don't listen on IPv6 by default. This PR attempts to fix this issue by adding IPv6 specific lines to the Nginx config templates.

listen 80; 
listen [::]:80;  # this line was missing

listen 127.0.0.1:80;
listen [::1]:80;  # this line was missing

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Deployment notes

agent setup nginx seems to be needed to update the configuration on all server types, unless another event updates it.
AAAA records should be added after making the server accept IPv6 requests.

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References

https://serverfault.com/questions/638367/do-you-need-separate-ipv4-and-ipv6-listen-directives-in-nginx/638370#638370
https://serverfault.com/questions/512054/globally-setting-ipv6only-off/512213#512213
https://stackoverflow.com/questions/40189084/what-is-ipv6-for-localhost-and-0-0-0-0/40189197#40189197
https://docs.aws.amazon.com/en_us/lightsail/latest/userguide/amazon-lightsail-configure-ipv6-on-nginx.html#configure-ipv6-nginx