fix: add environment variable POSTGRES_USER (#20786)

docker/docker-compose-template.yaml

@@ -85,6 +85,7 @@ services:
     restart: always
     environment:
       PGUSER: ${PGUSER:-postgres}
+      POSTGRES_USER: ${POSTGRES_USER:-postgres}
       POSTGRES_PASSWORD: ${POSTGRES_PASSWORD:-difyai123456}
       POSTGRES_DB: ${POSTGRES_DB:-dify}
       PGDATA: ${PGDATA:-/var/lib/postgresql/data/pgdata}