Add IPv6 support for local-resolvers substitution script

[alessfg]

Proposed changes

This PR ports the latest updates made to the upstream https://github.com/nginxinc/docker-nginx image. It adds IPv6 support for the local-resolvers substitution script and fixes some shell linter warnings.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the CONTRIBUTING document
• I have run ./update.sh and ensured all entrypoint/Dockerfile template changes have been applied to the relevant image entrypoint scripts & Dockerfiles
• I have tested that the NGINX Unprivileged Docker images build and run correctly on all supported architectures on an unprivileged environment (check out the README for more details)
• I have updated any relevant documentation (README)

[wanisfahmyDE]

hey @alessfg, is this PR fixed with the 1.25.4 release?
referring to this issue #114

[alessfg]

Not quite. That issue is caused by replacing the default.conf file with a different one before the script runs. This PR fixes an issue that led to IPv6 addresses not being correctly templated even when using the "default" default.conf.

[wanisfahmyDE]

ah got it, thanks!
yea I guess that's actually the same issue we're currently facing. This Dockerfile is doing the same with this nginx.conf and running in an IPv6 only environment causes an: invalid port in resolver "xx:xxxx:xxxx::a" in /etc/nginx/conf.d/default.conf

Do you maybe know if there is a workaround to solve this issue while still running on IPv6?

Thanks

[alessfg]

The issue you are describing should have been fixed by this PR (you seem to be missing the IPv6 square brackets, which this PR addresses).

[wanisfahmyDE]

Thanks for the hint, this is really helpful. Since devlake uses a custom script for startup https://github.com/apache/incubator-devlake/blob/main/config-ui/nginx.sh#L27, I will submit a PR there to match the changes from this PR.