Log client IP in gitlab-pages

We are currently not propagating the client IP for TLS traffic through HAProxy, which makes correlation quite cumbersome.

Steps needed:

• PROXY protocol support in gitlab-pages (gitlab-org/gitlab-pages!278 (merged))
• Support for -listen-https-proxyv2 in omnibus (gitlab-org/omnibus-gitlab!4760 (merged))
• Support for send-proxy-v2 in haproxy (gitlab-cookbooks/gitlab-haproxy!256 (merged))
• Enable -listen-https-proxyv2 in chef-repo on gstg (https://ops.gitlab.net/gitlab-cookbooks/chef-repo/-/merge_requests/4715)
• Switch pages haproxy backend to send-proxy-v2 on gstg (https://ops.gitlab.net/gitlab-cookbooks/chef-repo/-/merge_requests/4716)
• Enable -listen-https-proxyv2 in chef-repo on gprd (https://ops.gitlab.net/gitlab-cookbooks/chef-repo/-/merge_requests/4783)
• Switch pages haproxy backend to send-proxy-v2 on gprd (https://ops.gitlab.net/gitlab-cookbooks/chef-repo/-/merge_requests/4784)

See also gitlab-org/gitlab-pages#180 (closed).