Cloudflare: Remove HAProxy keepalive workaround

After https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/9709 we should remove the workaround we added in production#1863 (closed).

For this we need to:

• adapt HAProxy to log the IP from the header, not src
• disable HAProxy side rate-limiting (otherwise, we re-trigger the bug)
• disable Keepalive workaround

The latter two are config changes via node-attributes and should be done in the same MR to the chef-repo.