Fix `-d /Root` in `ydb admin cluster dump`

[pixcc]

ydb --profile cluster admin cluster dump --output ~/backup1
2025-03-21T14:30:32.136845Z :INFO: Backup cluster to "/home/bastion/backup1"
2025-03-21T14:30:32.138501Z :INFO: Backup cluster root "/Root" to /home/bastion/backup1
2025-03-21T14:30:32.207451Z :INFO: Backup database "/Root/testdb" to "/home/bastion/backup1/Root/testdb"
2025-03-21T14:30:32.220153Z :ERROR: Backup failed
Status: SCHEME_ERROR
Issues:
<main>: Error: Type annotation, code: 1030
    <main>:1:1: Error: At function: KiReadTable!
        <main>:1:1: Error: Cannot find table 'db.[/Root/testdb/.sys/auth_group_members]' because it does not exist or you do not have access permissions. Please check correctness of table path and user permissions., code: 2003

Don't forget to merge to 25-1