Added transaction feature, fixed some mistakes

backend/migrations/000002_create_families.up.sql

@@ -3,7 +3,7 @@ CREATE TABLE families
     id                 BIGSERIAL PRIMARY KEY,
     name               TEXT      NOT NULL,
     owner_id           BIGINT    NOT NULL REFERENCES users (id),
-    telegram_chat_id   BIGINT    NOT NULL,
+    telegram_chat_id   BIGINT,
     telegram_chat_name TEXT,
     created_at         TIMESTAMP NOT NULL DEFAULT NOW(),
     updated_at         TIMESTAMP NOT NULL DEFAULT NOW()