Suggest A DNS records instead of CNAME for custom gitlab pages domains

Problem to solve

The information on setting up your domain and subdomain is incorrect. The UI and documentation indicates creating a DNS record of type CNAME that points to your username. To verify a domain we also need a TXT record as well. Using a CNAME type can lead to domain being unable to be verified and violates the rule that If a CNAME RR is present at a node, no other data should be present.

Proposal

Update the UI and documentation to recommend an A record.

Update the documentation for creating a subdomain to recommend an A record. https://docs.gitlab.com/ee/user/project/pages/custom_domains_ssl_tls_certification/index.html#for-subdomains

What does success look like, and how can we measure that?

• Increased adoption of pages
• Improved user experience
• Reduced confusion in domain verification