Deleting the `Backup` resource doesn't delete the backup files from the MinIO bucket

[shajia-deshaw]

cc: @Agalin

[Agalin]

This is not possible with pgbackrest. It doesn't provide any way to remove a specific backup, only retention by time or count and handles expiration of files on its end. Manual removal of files from the bucket is a bad idea.

[Agalin]

Reopening as I've learned that pgbackrest actually supports expiring a specific backup since version 2.27. It's definitely something we'd like to support.