refactor: updated swagger;

feat: helper function in errors for checking postgres error types;
feat: sql query method for finding users by their email;
feat: registration begin/complete with checking existing username/email;
refactor: error handling in controller

docker-compose.yml

@@ -19,6 +19,7 @@ services:
       POSTGRES_URL: ${POSTGRES_URL}
       REDIS_URL: ${REDIS_URL}
       MINIO_URL: ${MINIO_URL}
+      ENVIRONMENT: ${ENVIRONMENT}
     ports:
       - "8080:8080"
     networks: