get_structure endpoint

sql/get_folders.sql

@@ -0,0 +1,11 @@
+SELECT
+    f.folder_id,
+    owner_id,
+    folder_name,
+    created_at
+FROM
+    folders f
+    JOIN permissions p ON f.folder_id = p.folder_id
+WHERE
+    parent_folder_id = $1
+    AND p.user_id = $2