chore: Add note about postgresql18 path change to v2.51 upgrade notes. (#13498)

Author: pageinsec

docs/content/en/open_source/upgrading/2.51.md

@@ -68,6 +68,8 @@ Sometimes it's easier to just perform the upgrade manually, which would look som
 It may need some tuning to your specific needs and docker compose setup. The guide is loosely based on https://simplebackups.com/blog/docker-postgres-backup-restore-guide-with-examples.
 If you already have a valid backup of the postgres 16 database, you can start at step 4.
 
+_Note: If you are using a bound volume, the path has changed for Postgres18. It is now `/var/lib/postgresql/` instead of `/var/lib/postgresql/data`. Failure to change the path may result in errors about failure to create a shim task. See the discussion in [docker-library/postgres](https://github.com/docker-library/postgres/issues/1370)._
+
 ### 0. Backup
 
 Always back up your data before starting and save it somewhere.