docs: correct the Redis and Valkey pages' key, prefix, Sentinel and log-level claims against the code

[silentoplayz]

Summary

I compared the Redis and Valkey pages with the env code, the Redis helper and the socket manager.

• Redis holds token revocations, socket pools, locks, tasks and rate limits. Persisted configuration lives in the database config table, so the open-webui:config:* example is gone, "cached configuration" now names the cached tool server and terminal server lists, and the key examples are real ones (the websocket pools sit in the WEBSOCKET_REDIS_URL database).
• The cluster-mode {prefix}: hash-slot formatting does not exist. The prefix is used verbatim, and open-webui is already the default.
• The prerequisite "version 1.0 or higher" is replaced, because there is no Open WebUI v1.0 release.
• The Sentinel section now says how Sentinel is enabled (REDIS_SENTINEL_HOSTS, REDIS_SENTINEL_PORT and the websocket twins) and that the URL's hostname is the master name. WEBSOCKET_REDIS_URL and WEBSOCKET_REDIS_CLUSTER inherit their REDIS_* values when unset. The verification log line is written at DEBUG level.
• Valkey: the example command now carries the --appendonly yes --maxmemory-policy noeviction flags the Redis page it defers to calls critical (eviction policy) and recommends for production (AOF).

Related issue or discussion

None.

Checklist

• I have reviewed the relevant documentation and matched the existing style.
• This PR meets Open WebUI's contribution standards: it is accurate, relevant to users, narrowly scoped, maintainable, and not promotional content, advertising, lead generation, SEO placement, or a request to list a product, service, provider, integration, gateway, tool, or company primarily for visibility.
• I understand that PRs that do not meet these standards may be closed without review and will not be merged. Repeated, low-quality, off-topic, promotional, or intentionally misleading submissions may result in the contributor being blocked from future participation in Open WebUI repositories.

Notes for reviewers

Sources on dev: models/config.py, env.py (REDIS_KEY_PREFIX, REDIS_SENTINEL_*, WEBSOCKET_*), utils/redis.py, socket/main.py (the debug log line), and a search of every REDIS_KEY_PREFIX key in the backend.