fix: postgresql container volume

Reviewed-on: #7
Co-authored-by: Jarno Kiesiläinen <jarnokie@gmail.com>
Co-committed-by: Jarno Kiesiläinen <jarnokie@gmail.com>

local-dev/compose.yml

@@ -8,4 +8,7 @@ services:
       POSTGRES_PASSWORD: vibing
       POSTGRES_DB: vibing
     volumes:
-      - postgres_data:/var/lib/postgresql/data
+      - postgres_data:/var/lib/postgresql/data
+
+volumes:
+  postgres_data: