Add version attributes for 8.13.0

[joepeeples]

Contributes to https://github.com/elastic/dev/issues/2505 by adding version attributes for 8.13.0.

[github-actions]

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[bmorelli25]

LGTM.

Posting here too: This doesn't bump the docs version, it just adds the new version files. Feel free to merge whenever!