Revert "Upgrade Postgres to 18-alpine and fix volume mount. Closes #3272 (#3275)"

This reverts commit ce562a1.

Author: mlodic

docker/env_file_postgres_template

@@ -1,4 +1,3 @@
 POSTGRES_PASSWORD=password
 POSTGRES_USER=user
-POSTGRES_DB=intel_owl_db
-PGDATA=/var/lib/postgresql/pgdata
+POSTGRES_DB=intel_owl_db

docker/postgres.override.yml

@@ -1,10 +1,10 @@
 services:
 
   postgres:
-    image: library/postgres:18-alpine
+    image: library/postgres:16-alpine
     container_name: intelowl_postgres
     volumes:
-      - postgres_data:/var/lib/postgresql
+      - postgres_data:/var/lib/postgresql/data/
     env_file:
       - ./env_file_postgres
     healthcheck: