postgres: add option to cloudctl postgres delete to also delete the referenced backup-config

[FrankEppink]

an option for cloudctl postgres delete ... would be helpful to also delete the referenced backup-config.

Obviously the actual deletion of the backup-config should only be done, when the backup-config is only referenced by the to-be-deleted postgres(let) and has no other postgres(lets) using it.

[eberlep]

I find that a bit dangerous. If you, by accident, remove the wrong database, you also remove all existing backups. So you wipe all your data with one command.

I am open to discussions, but I would like to not implement this :-)

[FrankEppink]

Does deletion of a backup-config mean that all related backups are deleted? If yes I agree this would be far too dangerous.

An alternative would be to introduce an additional option for cloudctl postgres backup-config list, e.g.

cloudctl postgres backup-config list --orphaned