Alerting: Fix file import/export of recording rules with target datasource uid (#115663)

Alerting: Fix export of recording rules with target datasource uid

pkg/tests/api/alerting/test-data/rulegroup-1-post.json

@@ -53,6 +53,26 @@
         "exec_err_state": "Alerting",
         "missing_series_evals_to_resolve": 2
       }
+    },
+    {
+      "grafana_alert": {
+        "title": "RecordingRule1",
+        "data": [
+          {
+            "refId": "A",
+            "datasourceUid": "__expr__",
+            "model": {
+              "expression": "1 + 1",
+              "type": "math"
+            }
+          }
+        ],
+        "record": {
+          "metric": "test_metric",
+          "from": "A",
+          "target_datasource_uid": "test-datasource-uid"
+        }
+      }
     }
   ]
 }