Fix/improve cloud hosted release note xlinks

[shainaraskas]

Our pre-2025 release notes are here: https://www.elastic.co/guide/en/cloud-hosted/current/index.html

but we don't link to them from our cloud hosted release notes landing page: https://www.elastic.co/docs/release-notes/cloud-hosted/

and our deprecations page DOES link to previous versions, but links to the old /cloud/ book, resulting in a circular redirect: https://www.elastic.co/docs/release-notes/cloud-hosted/deprecations

todo: add very visible callout on all pages (can reuse) and also fix the link we have / replace the callout with the broken link