GitLab Pages: Add support for namespace-in-path parameter in NGINX

Summary

GitLab Pages is adding support for running without a DNS wildcard certificate. To enable this, a new paramater named namespace-in-path was added that allows the namespace to be in the URL path instead of the domain.

To make this work in Charts, it looks like we may need some advanced NGINX configuration.

Context

• GitLab Pages without DNS wildcard - MVC (gitlab-org/gitlab#17584 - closed)
• Tech Eval: GitLab Pages without DNS wildcard (N... (gitlab-org/gitlab#211677 - closed)
• Initial draft implementation: Add namespace-in-path parameter for GitLab Pages (!3491 - closed)

Matching Omnibus change:

• gitlab-org/omnibus-gitlab!7250 (merged)
• gitlab-org/omnibus-gitlab!7324 (merged)
• gitlab-org/omnibus-gitlab!7425 (merged)