Add Elasticsearch release notes

[lcawl]

This PR copies the Elasticsearch release notes and breaking changes from elastic/elasticsearch#122884 into the Installation and Upgrade Guide.

It also fixes links from the breaking changes page to the appropriate release note pages and removes "beta1" from the URLs so that these pages can be used for rc1 and rc2 release details too.

[github-actions]

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[mergify]

This pull request is now in conflict. Could you fix it @lcawl? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch <remote-repo>
git checkout -b 90beta1-es <remote-repo>/90beta1-es
git merge <remote-repo>/9.0
git push <remote-repo> 90beta1-es

[mergify]

This pull request is now in conflict. Could you fix it @lcawl? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch <remote-repo>
git checkout -b 90beta1-es <remote-repo>/90beta1-es
git merge <remote-repo>/9.0
git push <remote-repo> 90beta1-es