fix: pattern persistence feature flag

[trevorwhitney]

What this PR does / why we need it:

There was a typo in #18214 that set the pattern writer instance as metricsWriter, causing patternWriter to always be nil, which is why we are no longer seeing patterns in ops where the are enabled.

Also, due to the bug #18214 was fixing, which resulted in pattern persistence being enabled in production prematurely, we now have customers who have persisted patterns that we don't want them to query until we fix grafana/logs-drilldown#1355 and #18213, so this PR also adds logic to only query persisted patterns when the feature flag is enabled as well.

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• Title matches the required conventional commits format, see here
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