updating cloud for release notes in asciidoc

[georgewallace]

Updating the conf.yaml for the cloud release notes that will be staying in asciidoc.

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[georgewallace]

@KOTungseth PR for the docs repo for the release notes. I think I got this right.

[lcawl]

If the builds pass, LGTM

[lcawl]

Seeing all these broken links makes me question whether rather than removing all the pages from https://www.elastic.co/guide/en/cloud/current/index.html (except release notes) is the right path forward or whether it's simpler to just create a "new" book that contains only the release notes. Since redirects are being created for all those pages, IMO that saves us from having to do all this clean up of broken links. I've created #3202 to test that alternative