backup: reorder tables in order of dependency

backup: reorder tables in order of dependency

Currently we dump the tables manually and print the relevant DDL
statements into the dump-file before copying the data.

The complete backup and dump specific tables part would probably be
best replaced by an appropriate `pg_dump` invocation - but as a
stop-gap measure reorder the tables in order of their dependencies.

Noticed while adding a foreign key constraint on 2 new tables
(objectgroup_attribute and rule_attribute) and running backup+restore.

Reported-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Tested-by: Dominik Csapak <d.csapak@proxmox.com>
Reviewed-by: Dominik Csapak <d.csapak@proxmox.com>