DEV: add 8.10 what's new page

[dwdougherty]

This is a Redis 8.10 feature.

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Note

Low Risk
Documentation-only changes with no runtime or application code impact.

Overview
Adds a new Redis 8.10 what's-new page and wires it into the Develop docs navigation.

The new page documents 8.10 vs 8.8: hash templates; list/set/stream commands (LMOVEM/BLMOVEM, SUNIONCARD/SDIFFCARD, XREAD/XREADGROUP reply caps); Search (FT.ALIASLIST, COLLECT, stricter TIMEOUT / RETURN_STRICT); JSONPath extensions; Time Series (TS.NRANGE, TS.READ, TS.QUERYLABELS, etc.); bug fixes; performance; Modules API; and CLI updates. develop/whats-new/_index.md gets a Q3 2026 section linking to 8.10, and redis-feature-sets.md lists 8.10 at the top of the table.

Older version pages (8.0–8.8) have weight increased by 1 so 8.10 (weight: 1) sorts first in the sidebar.

^{Reviewed by Cursor Bugbot for commit 15ac90f. Bugbot is set up for automated code reviews on this repo. Configure here.}

[github-actions]

DOC-6552

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-6552/develop/whats-new/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-0/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-10/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-2/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-4/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-6/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/8-8/
https://redis.io/docs/staging/DOC-6552/develop/whats-new/redis-feature-sets/