AAP-16926 Delete unpartitioned tables in a separate transaction

[AlanCoding]

SUMMARY

My prior merge #14055 broke cleanup jobs, and this is me trying to fix that.

The issue is pretty high level:

https://stackoverflow.com/questions/12838111/django-db-migrations-cannot-alter-table-because-it-has-pending-trigger-events

Every migration is inside a transaction. In PostgreSQL you must not update the table and then alter the table schema in one transaction.

And what we saw were errors of this type:

django.db.utils.InternalError: could not find trigger 17121

That error is really hard to make sense of. Within my process of troubleshooting this issue, I tried to manually drop all the constraints on the unpartitioned tables before dropping them. That led to this interesting error:

psycopg.errors.ObjectInUse: cannot ALTER TABLE "main_host" because it has pending trigger events

That starts to jive really well with the above statement that "you must not update the table and then alter the table schema".

ISSUE TYPE

• Bug, Docs Fix or other nominal change

COMPONENT NAME

• API