fix: add database name to postgres healthcheck (#203)

When POSTGRES_USER differs from POSTGRES_DB, pg_isready defaults to
connecting to a database named after the user, causing healthcheck
to fail with "database does not exist".

docker-compose.postgres.yml

@@ -19,7 +19,7 @@ services:
     volumes:
       - postgres-data:/var/lib/postgresql
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-goclaw}"]
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-goclaw} -d ${POSTGRES_DB:-goclaw}"]
       interval: 5s
       timeout: 5s
       retries: 10