Improvement for default `list_instances_in_vault_command` command

[theboringstuff]

Describe the bug
Currently default command for list_instances_in_vault_command is not following expected contract. It uses ls -la, which prints directory content with a lot of additional metadata, like file permissions, owners, size, and also shows hidden files, for example

$ ls -la /backup-storage/granular/20250624T094831
total 24
drwxr-xr-x    4 10001    root          4096 Jun 24 09:48 .
drwxr-xr-x    3 10001    root          4096 Jun 24 09:48 ..
-rw-r--r--    1 10001    root            81 Jun 24 09:48 .console
-rw-r--r--    1 10001    root            50 Jun 24 09:48 .metrics
drwxr-xr-x    2 10001    root          4096 Jun 24 10:03 _system
drwxr-xr-x    2 10001    root          4096 Jun 24 10:03 testdb 

This is not what backup daemon expects, it expects something like ls -1

$ ls -1  /backup-storage/granular/20250624T094831
_system
testdb  

Expected behavior
Default command should be meaningful at least in some cases, e.g. ls -1 %(data_folder)s