Add custom static IP key for Geo NGINX controller

What does this MR do?

Add custom static IP key for Geo NGINX controller

Adds `global.hosts.externalGeoIP` to set a static IP for the
Geo NGINX LoadBalancer, which previously used `global.hosts.externalIP`
like the default NGINX controller.

This allows to configure distinct static IPs for both NGINX subcharts.

Fixes https://gitlab.com/gitlab-org/charts/gitlab/-/issues/5006

Changelog: fixed

Background

In #4532 (closed), a second instance of the NGINX subchart for customized HTTP header handling for internal Geo traffic (needed for unified URLs). Both chart instances try pull their LoadBalancer IP from global.hosts.externalIP, resulting in only one LB remaining in Pending since its IP address is already bound.

Related issues

Closes #5006 (closed)

Author checklist

See Definition of done.

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

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, follow the instructions in the "Reviewer Roulette" section of the Danger Bot MR comment, as per the Distribution experimental MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added/updated
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Equivalent MR/issue for Gitlab Operator project opened (see Operator documentation on impact of Charts changes)
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.

Test Plan

1. Install a release and set global.hosts.externalIP.

   Expectation: The NGINX LB service is rendered with global.hosts.externalIP as LB IP.

2. Upgrade a release and enable:

   • the Geo controller (nginx-ingress-geo.enabled=true), and
   • set global.hosts.externalGeoIP.

   Expectation: The Geo NGINX LB service is rendered with global.hosts.externalGeoIP as LB IP.