AlertingNG/SSE: Datasource UID and UID/ID only (drop name) (#33039)

SSE still will support ID until dashboard/frontend always requests UID
update *.http examples

Co-authored-by: gotjosh <josue@grafana.com>

pkg/expr/nodes.go

@@ -30,7 +30,7 @@ type rawNode struct {
 func (rn *rawNode) GetDatasourceName() (string, error) {
 	rawDs, ok := rn.Query["datasource"]
 	if !ok {
-		return "", fmt.Errorf("no datasource in query for refId %v", rn.RefID)
+		return "", nil
 	}
 	dsName, ok := rawDs.(string)
 	if !ok {
@@ -39,6 +39,18 @@ func (rn *rawNode) GetDatasourceName() (string, error) {
 	return dsName, nil
 }
 
+func (rn *rawNode) GetDatasourceUid() (string, error) {
+	rawDs, ok := rn.Query["datasourceUid"]
+	if !ok {
+		return "", nil
+	}
+	dsUID, ok := rawDs.(string)
+	if !ok {
+		return "", fmt.Errorf("expected datasource identifier to be a string, got %T", rawDs)
+	}
+	return dsUID, nil
+}
+
 func (rn *rawNode) GetCommandType() (c CommandType, err error) {
 	rawType, ok := rn.Query["type"]
 	if !ok {