RS: Added note that upgrading existing Active-Active DBs to Redis 8 will not automatically enable JSON

[rrelledge]

Staged previews:

1. https://redis.io/docs/staging/DOC-6358/operate/rs/release-notes/rs-8-0-releases/rs-8-0-2-17/#built-in-capabilities-with-redis-8
2. https://redis.io/docs/staging/DOC-6358/operate/rs/databases/configure/#capabilities

Note

Low Risk
Low risk documentation-only change; it clarifies module enablement behavior for Active-Active upgrades and could only impact reader expectations if incorrect.

Overview
Clarifies in the Redis 8 built-in capabilities tables that JSON is not automatically enabled when upgrading existing Active-Active databases to Redis 8.

Adds a footnote to both the reusable embed (content/embeds/rs-8-enabled-modules.md) and the 8.0.2-17 release notes stating that only newly created Active-Active databases on Redis 8 enable JSON by default.

^{Written by Cursor Bugbot for commit 5053344. This will update automatically on new commits. Configure here.}

[github-actions]

DOC-6358

[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-6358/operate/rs/release-notes/rs-8-0-releases/rs-8-0-2-17/

[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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^{Security scan by Jit}

[andy-stark-redis]

LGTM