Alerting/metrics (#33547)

* moves alerting metrics to their own pkg

* adds grafana_alerting_alerts (by state) metric

* alerts_received_{total,invalid}

* embed alertmanager alerting struct in ng metrics & remove duplicated notification metrics (already embed alertmanager notifier metrics)

* use silence metrics from alertmanager lib

* fix - manager has metrics

* updates ngalert tests

* comment lint
Signed-off-by: Owen Diehl <ow.diehl@gmail.com>

* cleaner prom registry code

* removes ngalert global metrics

* new registry use in all tests

* ngalert metrics impl service, hack testinfra code to prevent duplicate metric registrations

* nilmetrics unexported

pkg/tests/testinfra/testinfra.go

@@ -16,7 +16,9 @@ import (
 	"github.com/grafana/grafana/pkg/models"
 	"github.com/grafana/grafana/pkg/registry"
 	"github.com/grafana/grafana/pkg/server"
+	"github.com/grafana/grafana/pkg/services/ngalert/metrics"
 	"github.com/grafana/grafana/pkg/services/sqlstore"
+	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"gopkg.in/ini.v1"
@@ -26,8 +28,10 @@ import (
 // The server address is returned.
 func StartGrafana(t *testing.T, grafDir, cfgPath string, sqlStore *sqlstore.SQLStore) string {
 	t.Helper()
-
 	ctx := context.Background()
+	// Prevent duplicate registration errors between tests by replacing
+	// the registry used.
+	metrics.GlobalMetrics.SwapRegisterer(prometheus.NewRegistry())
 
 	origSQLStore := registry.GetService(sqlstore.ServiceName)
 	t.Cleanup(func() {