Nginx should listen on IPv6 addresses in addition to IPv4

[9numbernine9]

Is your feature request related to a problem? Please describe.
In an IPv6-only environment (e.g. an IPv6-only Kubernetes cluster), it's not possible to connect to a Snappymail pod on port 8888. This appears to be due to nginx.conf being configured only with an IPv4 listen directive.

Describe the solution you'd like
In addition, to an IPv4 listen directive, add an IPv6 listen directive as well.

Currently in nginx.conf:

server {
    listen 8888;
    root /snappymail;
    index index.php;
    charset utf-8;

Preferred Suggestion:

server {
    listen 8888;
    listen [::]:8888;
    root /snappymail;
    index index.php;
    charset utf-8;

Describe alternatives you've considered
N/A

Additional context
N/A

[9numbernine9]

Thanks for the quick fix @the-djmaze !