Document new optimistic locking commands in Redis 8.4

[LiorKogan]

Added information about new atomic commands in Redis 8.4 for compare-and-set and compare-and-delete operations.

---

Note

Low Risk
Low risk documentation-only change; potential risk is limited to minor inaccuracies/formatting in the newly added command references.

Overview
Updates the Transactions documentation to note that Redis 8.4 adds single-command atomic alternatives to WATCH/MULTI optimistic locking for string keys.

Specifically documents using SET with IFEQ/IFNE/IFDEQ/IFDNE for compare-and-set and DELEX for compare-and-delete when the value (or digest) hasn’t changed since it was fetched.

^{Written by Cursor Bugbot for commit 0889d48. This will update automatically on new commits. Configure here.}

[github-actions]

Staging links:
https://redis.io/docs/staging/LiorKogan-patch-1/develop/using-commands/transactions/

[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

---

^{Security scan by Jit}

[dwdougherty]

Thank you, @LiorKogan!