Update the "on-call documentation" link URL on the Production page.
This makes the "on-call documentation" link URL at https://about.gitlab.com/handbook/engineering/infrastructure/production/#on-call-support root-relative.
cc @cindy
This makes the "on-call documentation" link URL at https://about.gitlab.com/handbook/engineering/infrastructure/production/#on-call-support root-relative.
cc @cindy