Add support for .meta.json files associated with .txt files

src/snapshot_middleware/snapshots/test__instance_from_imfs.snap

@@ -9,6 +9,7 @@ metadata:
     Path: /foo.txt
   relevant_paths:
     - /foo.txt
+    - /foo.meta.json
 name: foo
 class_name: StringValue
 properties:

src/snapshot_middleware/snapshots/test__project_with_path_to_txt.snap

@@ -9,6 +9,7 @@ metadata:
     Path: /foo/default.project.json
   relevant_paths:
     - /foo/other.txt
+    - /foo/other.meta.json
     - /foo/default.project.json
 name: path-project
 class_name: StringValue