extracts alertmanager from DI, including migrations (#34071)

* extracts alertmanager from DI, including migrations

* includes alertmanager Run method in ngalert

* removes 3s test shutdown timeout

* lint

pkg/tests/testinfra/testinfra.go

@@ -10,7 +10,6 @@ import (
 	"path/filepath"
 	"strings"
 	"testing"
-	"time"
 
 	"github.com/grafana/grafana/pkg/infra/fs"
 	"github.com/grafana/grafana/pkg/models"
@@ -66,8 +65,6 @@ func StartGrafana(t *testing.T, grafDir, cfgPath string, sqlStore *sqlstore.SQLS
 		}
 	}()
 	t.Cleanup(func() {
-		ctx, cancel := context.WithTimeout(ctx, 3*time.Second)
-		defer cancel()
 		if err := server.Shutdown(ctx, "test cleanup"); err != nil {
 			t.Error("Timed out waiting on server to shut down")
 		}