fix: proper URLs in all updates.jenkins.io pages#909

lemeurherve wants to merge 4 commits intojenkins-infra:masterjenkins-infra/update-center2:masterfrom

lemeurherve:helpdesk4882-absolute-links-in-header-and-footerlemeurherve/update-center2:helpdesk4882-absolute-links-in-header-and-footerCopy head branch name to clipboard