Add postgres volume (#100)

Author: Mariatta

compose.yml

@@ -15,6 +15,7 @@ services:
       interval: 1s
     volumes:
       - ./docker-compose/postgres/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d
+      - pgdata:/var/lib/postgresql/data
 
   redis:
     image: redis:7-bullseye
@@ -53,3 +54,6 @@ services:
     ports:
       - "1080:1080"
       - "1025:1025"
+
+volumes:
+  pgdata: