docs: Deprecate old Copilot metrics endpoints closed on April 2, 2026

The four legacy Copilot metrics endpoints
(GetEnterpriseMetrics, GetEnterpriseTeamMetrics,
GetOrganizationMetrics, GetOrganizationTeamMetrics) were closed down
on April 2, 2026 for github.com. Add Deprecated notices pointing users
to the replacement report methods while keeping the functions for any
GitHub Enterprise Server users who may still have access.

Fixes #4136

Author: qwdaiahaya780

github/copilot.go

@@ -491,6 +491,10 @@ func (s *CopilotService) GetSeatDetails(ctx context.Context, org, user string) (
 
 // GetEnterpriseMetrics gets Copilot usage metrics for an enterprise.
 //
+// Deprecated: This endpoint was closed down on April 2, 2026 for github.com.
+// It may still be available for GitHub Enterprise Server. Use GetEnterpriseDailyMetricsReport
+// or GetEnterpriseMetricsReport instead.
+//
 // GitHub API docs: https://docs.github.com/enterprise-cloud@latest/rest/copilot/copilot-metrics#get-copilot-metrics-for-an-enterprise
 //
 //meta:operation GET /enterprises/{enterprise}/copilot/metrics
@@ -517,6 +521,10 @@ func (s *CopilotService) GetEnterpriseMetrics(ctx context.Context, enterprise st
 
 // GetEnterpriseTeamMetrics gets Copilot usage metrics for an enterprise team.
 //
+// Deprecated: This endpoint was closed down on April 2, 2026 for github.com.
+// It may still be available for GitHub Enterprise Server. Use GetEnterpriseDailyMetricsReport
+// or GetEnterpriseMetricsReport instead.
+//
 // GitHub API docs: https://docs.github.com/enterprise-cloud@latest/rest/copilot/copilot-metrics#get-copilot-metrics-for-an-enterprise-team
 //
 //meta:operation GET /enterprises/{enterprise}/team/{team_slug}/copilot/metrics
@@ -543,6 +551,10 @@ func (s *CopilotService) GetEnterpriseTeamMetrics(ctx context.Context, enterpris
 
 // GetOrganizationMetrics gets Copilot usage metrics for an organization.
 //
+// Deprecated: This endpoint was closed down on April 2, 2026 for github.com.
+// It may still be available for GitHub Enterprise Server. Use GetOrganizationDailyMetricsReport
+// or GetOrganizationMetricsReport instead.
+//
 // GitHub API docs: https://docs.github.com/rest/copilot/copilot-metrics#get-copilot-metrics-for-an-organization
 //
 //meta:operation GET /orgs/{org}/copilot/metrics
@@ -569,6 +581,10 @@ func (s *CopilotService) GetOrganizationMetrics(ctx context.Context, org string,
 
 // GetOrganizationTeamMetrics gets Copilot usage metrics for an organization team.
 //
+// Deprecated: This endpoint was closed down on April 2, 2026 for github.com.
+// It may still be available for GitHub Enterprise Server. Use GetOrganizationDailyMetricsReport
+// or GetOrganizationMetricsReport instead.
+//
 // GitHub API docs: https://docs.github.com/rest/copilot/copilot-metrics#get-copilot-metrics-for-a-team
 //
 //meta:operation GET /orgs/{org}/team/{team_slug}/copilot/metrics