[v9.2.x] Expressions: Fixes the issue showing expressions editor (#62626)

* Expressions: Fixes the issue showing expressions editor (#62510)

* Use suggested value for uid

* update the snapshot

* use __expr__

* replace all -100 with __expr__

* update snapshot

* more changes

* revert redundant change

* Use expr.DatasourceUID where it's possible

* generate files

(cherry picked from commit 91221bc436)

* unit text fix

pkg/tests/api/alerting/api_notification_channel_test.go

@@ -20,6 +20,7 @@ import (
 	"github.com/prometheus/common/model"
 	"github.com/stretchr/testify/require"
 
+	"github.com/grafana/grafana/pkg/expr"
 	"github.com/grafana/grafana/pkg/models"
 	apimodels "github.com/grafana/grafana/pkg/services/ngalert/api/tooling/definitions"
 	ngmodels "github.com/grafana/grafana/pkg/services/ngalert/models"
@@ -968,7 +969,7 @@ func getRulesConfig(t *testing.T) string {
 							From: ngmodels.Duration(time.Duration(5) * time.Hour),
 							To:   ngmodels.Duration(time.Duration(3) * time.Hour),
 						},
-						DatasourceUID: "-100",
+						DatasourceUID: expr.DatasourceUID,
 						Model: json.RawMessage(`{
 							"type": "math",
 							"expression": "2 + 3 > 1"
@@ -1627,7 +1628,7 @@ const alertmanagerConfig = `
             }
           }
         ]
-      },   
+      },
 	  {
         "name": "slack_recv2",
         "grafana_managed_receiver_configs": [