Fix result of remote DB backup (#4229)

If you create a backup on Foreman+Katello Server or Smart Proxy
Servers by using "foreman-maintain backup [online|offline]",
foreman-maintain creates a dump of the database.

Regardless of the method (online or offline), the backup contains a dump
of the database.

Refs PR 893 in foreman_maintain

Tested on Foreman 3.14/Katello 4.16: Create an online/offline backup on
Foreman Server; migrate to external DB as documented; recreate an
online/offline backup on Foreman Server:

$ du -ksh /my-backup*
4.0G /my-backup-offline
4.0G /my-backup-online
5.2G /my-backup-post-migration-offline
5.2G /my-backup-post-migration-online
$ find /my-backup* -name "*.dump"
/my-backup-offline/foreman-backup-2025-09-10-07-36-30/candlepin.dump
/my-backup-offline/foreman-backup-2025-09-10-07-36-30/foreman.dump
/my-backup-offline/foreman-backup-2025-09-10-07-36-30/pulpcore.dump
/my-backup-online/foreman-backup-2025-09-10-07-48-17/candlepin.dump
/my-backup-online/foreman-backup-2025-09-10-07-48-17/foreman.dump
/my-backup-online/foreman-backup-2025-09-10-07-48-17/pulpcore.dump
/my-backup-post-migration-offline/foreman-backup-2025-09-10-11-45-19/candlepin.dump
/my-backup-post-migration-offline/foreman-backup-2025-09-10-11-45-19/foreman.dump
/my-backup-post-migration-offline/foreman-backup-2025-09-10-11-45-19/pulpcore.dump
/my-backup-post-migration-online/foreman-backup-2025-09-10-11-39-36/candlepin.dump
/my-backup-post-migration-online/foreman-backup-2025-09-10-11-39-36/foreman.dump
/my-backup-post-migration-online/foreman-backup-2025-09-10-11-39-36/pulpcore.dump

Note that the diff in size results to Foreman+Katello usage.

On Smart Proxy Server:

$ du -ksh /my-backup*
1.1G /my-backup-offline
1.1G /my-backup-online
$ find /my-backup* -name "*.dump"
/my-backup-online/foreman-proxy-backup-2025-09-10-07-42-49/pulpcore.dump
/my-backup-offline/foreman-proxy-backup-2025-09-10-07-48-45/pulpcore.dump

If you use a local PostgreSQL database, the "postgres" user does not
need write access to your backup target directory.

(cherry picked from commit 7e80375)

Author: maximiliankolb

guides/common/modules/proc_performing-a-full-backup.adoc

@@ -44,13 +44,9 @@ If you want to set a custom directory name, add the `--preserve-directory` optio
 The backup is then stored in the directory you provide in the command line.
 If you use the `--preserve-directory` option, no data is removed if the backup fails.
 
-Note that if you use a local PostgreSQL database, the `postgres` user requires write access to the backup directory.
-
 .Remote databases
 You can use the `{foreman-maintain} backup` command to back up remote databases.
 
-You can use both online and offline methods to back up remote databases, but if you use offline method, the `{foreman-maintain} backup` command performs a database dump.
-
 .Backing up to a remote NFS share
 To enable {Project} to save the backup to an NFS share, ensure that the `root` user of your {ProjectServer} or {SmartProxyServer} can write to the NFS share.
 NFS export options such as `root_squash` and `all_squash` are known to prevent this.