service: fix for disabled internal metrics.

Update of the internal metrics for Grafana was
disabled by mistake when refactoring the code.

Fixes #15651

pkg/cmd/grafana-server/server.go

@@ -31,6 +31,7 @@ import (
 	_ "github.com/grafana/grafana/pkg/infra/metrics"
 	_ "github.com/grafana/grafana/pkg/infra/serverlock"
 	_ "github.com/grafana/grafana/pkg/infra/tracing"
+	_ "github.com/grafana/grafana/pkg/infra/usagestats"
 	_ "github.com/grafana/grafana/pkg/plugins"
 	_ "github.com/grafana/grafana/pkg/services/alerting"
 	_ "github.com/grafana/grafana/pkg/services/auth"