update link for docs

Author: jinja2

docs/system/k8s-metrics.md

@@ -2160,4 +2160,4 @@ The value represents the current observed total usage of the resource in the nam
 
 [DocumentStatus]: https://opentelemetry.io/docs/specs/otel/document-status
 [MetricRecommended]: /docs/general/metric-requirement-level.md#recommended
-[MetricOptIn]: /docs/general/metric-requirement-level.md#optin
+[MetricOptIn]: /docs/general/metric-requirement-level.md#opt-in