add database migration and UserRepository wrapper

- implemented DB migration

- added UserRepository for DB interactions

- inserted initial test record

CMakeLists.txt

@@ -22,6 +22,9 @@ add_executable(auth_service
     src/http/controllers/health_controller.cpp
     src/db/sqllite_db.cpp
     src/db/statement.cpp
+    src/db/transaction.cpp
+    src/db/migrations_runner.cpp
+    src/repo/user_repository.cpp
 )
 
 target_include_directories(auth_service