Breaking: Default to Gateway API and Envoy Gateway

What does this MR do?

Breaking: Default to Gateway API and Envoy Gateway

Default to Gateway API and the bundled Envoy Gateway. NGINX Ingress is deprecated and is not supported anymore, but remains available until it's full removal in GitLab 20.0.

Related deprecation announcements:

• https://docs.gitlab.com/update/deprecations/#support-for-nginx-ingress-haproxy-and-traefik-charts
• https://docs.gitlab.com/update/deprecations/#support-for-nginx-ingress

Changelog: changed

Relates gitlab-com/gl-infra/software-delivery/operate#5 (closed)

Relates #6414 (closed)

Related issues

Author checklist

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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.