Add healthcheck for postgres

regarding #58

docker-compose.tmpl.yml

@@ -311,6 +311,11 @@ services:
       POSTGRES_DB: greenlight
       POSTGRES_USER: postgres
       POSTGRES_PASSWORD: password
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U postgres"]
+      interval: 10s
+      timeout: 5s
+      retries: 5
     volumes:
       - ./postgres-data:/var/lib/postgresql/data
 {{end}}