use ghcr.io for backupimage (#6333)

* use ghcr.io for backup image

* backup script: use renamed script + improved build of image

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Co-authored-by: DerLinkman <niklas.meyer@servercow.de>

helper-scripts/backup_and_restore.sh

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 
-DEBIAN_DOCKER_IMAGE="mailcow/backup:latest"
+DEBIAN_DOCKER_IMAGE="ghcr.io/mailcow/backup:latest"
 
 if [[ ! -z ${MAILCOW_BACKUP_LOCATION} ]]; then
   BACKUP_LOCATION="${MAILCOW_BACKUP_LOCATION}"