Add warning for deprecated endpoints (#54255)

Author: isaacmbrown

content/rest/copilot/copilot-usage.md

@@ -1,6 +1,6 @@
 ---
 title: REST API endpoints for GitHub Copilot usage metrics
-shortTitle: Copilot usage 
+shortTitle: Copilot usage
 intro: 'Use the REST API to access {% data variables.product.prodname_copilot_short %} usage metrics for an enterprise, an organization, or a team.'
 redirect_from:
   - /early-access/copilot/copilot-usage-api
@@ -13,4 +13,12 @@ autogenerated: rest
 allowTitleToDifferFromFilename: true
 ---
 
+<!-- expires 2025-03-01 -->
+
+<!-- When this expires, change the message to say they're no longer accessible at all -->
+
+>[!WARNING] These endpoints are closing down. They will be accessible throughout February 2025, but will not return any new data after February 1st. They will be retired on March 1st. **Please migrate to the [AUTOTITLE](/rest/copilot/copilot-metrics) as soon as possible.**
+
+<!-- end expires 2025-03-01 -->
+
 <!-- Content after this section is automatically generated -->