fix: postgres database user becomes orphaned after database deletion

[alehostert]

When deleting a PostgreSQL database using os db delete, the associated database user becomes orphaned and cannot be deleted afterwards using os db delete-user.

Steps to Reproduce

1. Create a PostgreSQL database:

   os db create --db-type postgresql --db-name mydatabase

2. Create a user with privileges on that database:

   os db create-user --db-type postgresql --db-name mydatabase --username myuser --password mypassword --privileges all

3. Delete the database:

   os db delete --db-type postgresql --db-name mydatabase

4. Verify the user still exists but has no database:

   os db get -t postgres -u myuser

   Returns empty databases array:

   {
     "status": "success",
     "body": {
       "pagination": {
         "pageNumber": 0,
         "itemsPerPage": 10,
         "pagesTotal": 0,
         "itemsTotal": 0
       },
       "databases": []
     }
   }

5. Try to delete the orphaned user:

   os db delete-user --db-type postgresql --db-name mydatabase --db-username myuser

   {
     "status": "infraError",
     "body": "DatabaseNotFound"
   }

   os db delete-user --db-type postgresql --db-username myuser

   Error: required flag(s) "db-name" not set

Expected Behavior

The orphaned user should be deletable, by allowing os db delete-user to work without requiring --db-name when the database no longer exists.

Workaround

Before deleting the database, run:

psql -U postgres -d mydatabase -h 127.0.0.1 -c "DROP OWNED BY myuser;"
os db delete-user --db-type postgresql --db-name mydatabase --db-username myuser
os db delete --db-type postgresql --db-name mydatabase

This ensures all objects owned by the user are dropped before attempting to delete the user.