Add GitLab Pages chart

What does this MR do?

Create a GitLab Pages chart using the CNG image being created in gitlab-org/build/CNG!553 (merged)

Scope:

• Implement a basic chart for GitLab Pages
• Does not provide support for custom domains
• Does not provide support for authenticated access

Testing

1. Bring your own wildcard certificate for *.pages.<k8s domain>, and make it a k8s tls secret.

2. Deploy a cluster with the following values

   global:
     hosts:
       domain: <k8s domain>
       externalIP: <external IP>
     imagePullPolicy: Always
     pages:
       enabled: true
   gitlab:
     gitlab-pages:
       ingress:
         tls:
           secretName: <secret with a wildcard HTTPS certificate for `*.pages.<k8s domain>`

Related issues

Closes: #2441 (closed)

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

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened