Ensure `pgo delete cluster --keep-backups` honors its flag
Ensure `pgo delete cluster --keep-backups` honors its flag

Previously the `pgo delete cluster --keep-backups` flag was keeping
the backups available at the physical storage layer, but the persistent
volume claim (PVC) was disappearing, which in most environments would
make the backups inaccessible.

Additionally, while working on this patch, there were a few more
noticeable behaviors:

- Backups created by pg_dump were not being removed
- Some of the backup cleanup logic was not correct
- There was no clear distinction in cleaning up PVCs belonging to
PostgreSQL instances vs. the backups. This could lead to too many PVCs
being deleted, or not enough PVCs being deleted
- The backup jobs were not all being cleaned up, despite a claim in on
of the functions

This patch addresses the original issue that was described, ensuring
that the `--keep-backups` and `--keep-data` flags honor their
behaviors, and fixes the above aforementioned described issues to ensure
we can keep the backing file system happy.

Issue: [ch6669]

CrunchyData/postgres-operator,CrunchyData/postgres-operator