Update index.mdx (#4474)

updated the Action Metrics link to reference the specific metric vs the generic openmetrics link

Co-authored-by: Brian MacDonald <brian.macdonald@temporal.io>

Author: tlotemporal

docs/cloud/billing-and-usage/index.mdx

@@ -54,7 +54,7 @@ The Temporal Cloud Billing API is in [Pre-release](/evaluate/development-product
 - **[Actions in Workflow History](/cloud/actions-usage#actions-in-workflows):** Highlights Actions in a given Workflow History via the Temporal Cloud UI. Note that some Actions are not measured in Workflow histories.
     - Viewable by Account Owners, Global Admin and Namespace Admin, Developers and Read-only
 
-- **[Actions Metrics](/cloud/metrics/openmetrics):** A high cardinality billable action metric that include labels for Category, Action Type, Workflow Type and Namespace down to minute granularity.
+- **[Actions Metrics](/cloud/metrics/openmetrics/metrics-reference#temporal_cloud_v1_billable_action_count):** A high cardinality billable action metric that include labels for Category, Action Type, Workflow Type and Namespace down to minute granularity.
     - Viewable by creating a service account with the "Metrics Read-Only" role. See the [OpenMetrics](/cloud/metrics/openmetrics#api-key-authentication) page for more information.
 
 :::tip Support, stability, and dependency info