refractor structure project and add user endpoint

backend/app/core/constants.py

@@ -0,0 +1,9 @@
+from enum import Enum
+
+DB_NAMING_CONVENTION = {
+    "ix": "%(column_0_label)s_idx",
+    "uq": "%(table_name)s_%(column_0_name)s_key",
+    "ck": "%(table_name)s_%(constraint_name)s_check",
+    "fk": "%(table_name)s_%(column_0_name)s_fkey",
+    "pk": "%(table_name)s_pkey",
+}