Support for new GitLab Pages options: `-artifacts-server` and `-artifacts-server-timeout`
These are being introduced in gitlab-pages!44 (merged) to support this %10.0 feature: https://gitlab.com/gitlab-org/gitlab-ce/issues/34102
GitLab and Pages both need to be able to see the -artifacts-server
flag, as GitLab will need to make decisions based on the configuration of Pages (as it does now for whether to show pages-related config).
The timeout defaults to 10 seconds if not specified; we probably want to make it tweakable.
I'm happy to take this on.