add ccs support for 8.19 and 9.1 (#2129)

**DO NOT MERGE THIS PR UNTIL 9.1 / 8.19 RELEASE DAY**

Linked to https://github.com/elastic/developer-docs-team/issues/313
Added versions 8.19 and 9.1 to the table listing support for cross
cluster search. The following screenshot gives a preview of the change.

Added the 'applies_to' tag to signify GA for 9.1.


<img width="1682" height="1988" alt="FireShot Capture 007 -
Cross-cluster search - Elastic Docs - localhost"
src="https://github.com/user-attachments/assets/fa69860d-810e-4d10-8179-7a5c834f06cb"
/>

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Co-authored-by: Liam Thompson <[email protected]>

Author: ketkee-aryamane