Support `--format` on `incus admin sql`

[alex14641]

It would be useful for incus admin sql query output to be easily parsed by scripts. E.g:

incus admin sql --raw --raw-delimiter " " global "select key,value from storage_pools_config where key = 'source'"
source /spare/incus-6.6/data/disks/container.img
source /spare/incus-6.6/data/disks/vm.img

Here is a patch.
admin-sql.diff.txt