Updates the default Postgres to 15 for new installs

docker/compose/docker-compose.postgres-tika.yml

@@ -39,7 +39,7 @@ services:
       - redisdata:/data
 
   db:
-    image: docker.io/library/postgres:13
+    image: docker.io/library/postgres:15
     restart: unless-stopped
     volumes:
       - pgdata:/var/lib/postgresql/data