Allow to configure the chart for IPv6-only

What does this MR do?

Add support for IPv6-only clusters

• All GitLab subcharts now bind IPv6 compatibly listeners by default.
• KAS: Autodiscover own IP/host.
• Spamcheck: Fix loading of custom config.
• Go services: Use :{port} bind instead of 0.0.0.0:{port}. Both result in the same binds, but the later notation can be misleading.

The default configuration fits IPv4-only, IPv6-only and dual stack clusters.

Changelog: added

Related issues

Closes Deployment in a complete IPv6 only environment (#2778 - closed)

Author checklist

For general guidance, please follow our Contributing guide.

Required

For anything in this list which will not be completed, please provide a reason in the MR discussion.

• Merge Request Title and Description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• MR has a green pipeline.
• Documentation created/updated.
• Tests added/updated, and test plan for scenarios not covered by automated tests.
• Equivalent MR/issue for omnibus-gitlab opened.

Reviewers checklist

• MR has a green pipeline on https://gitlab.com/gitlab-org/charts/gitlab.
• Consider downstream impact to the Operator, as per evaluating impact from changes to GitLab Chart.

Test Plan

1. Confirm CI passes (our CI clusters use IPv4 only)

2. Setup a IPv6 (single stack) cluster.

   • Note: Some providers do not support IPv6 single stack cluster (e.g. GKE only supports dual stack). The config does not work out of the box on dual stack clusters, because of a known bug in webrick.

   • Example config for kind:

     kind: Cluster
     apiVersion: kind.x-k8s.io/v1alpha4
     networking:
       ipFamily: ipv6
     nodes:
     - role: control-plane
       extraPortMappings:
       - containerPort: 32080
         hostPort: 80
         listenAddress: "::"
       - containerPort: 32443
         hostPort: 443
         listenAddress: "::"
       - containerPort: 32022
         hostPort: 32022
         listenAddress: "::"

3. Deploy the chart with the sample IPv6 values and confirm that all services come up operational.

What I tested:

• Register a runner.
• Push a commit via HTTPS.
• Deploy a GitLab Pages site.
• Connect a KAS agent.