Mark project node as instigating source for instances from project

src/snapshot_middleware/snapshots/test__project_with_children.snap

@@ -16,6 +16,14 @@ children:
   - snapshot_id: ~
     metadata:
       ignore_unknown_instances: true
+      instigating_source:
+        ProjectNode:
+          - Child
+          - class_name: Model
+            children: {}
+            properties: {}
+            ignore_unknown_instances: ~
+            path: ~
       relevant_paths: []
     name: Child
     class_name: Model

src/snapshot_middleware/snapshots/test__project_with_path_to_project_with_children.snap

@@ -17,6 +17,14 @@ children:
   - snapshot_id: ~
     metadata:
       ignore_unknown_instances: true
+      instigating_source:
+        ProjectNode:
+          - SomeChild
+          - class_name: Model
+            children: {}
+            properties: {}
+            ignore_unknown_instances: ~
+            path: ~
       relevant_paths: []
     name: SomeChild
     class_name: Model