Upgrade GitLab Pages to v0.5.0

What does this MR do?

Upgrade GitLab Pages to v0.5.0

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Several new features in GitLab Pages, including CORS support. This is needed for a Trello powerup: https://gitlab.com/gitlab-org/gitlab-ce/issues/32042

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?