Feature Request: Include filesystem for snapshots

[cf-sewe]

I could not find a simple way to generate graphs per ZFS filesystem and their snapshot usage.

The metric currently looks like this:

zfs_dataset_logical_used_bytes{name="rpool/application@zrepl_20220407_154137_000",pool="rpool",type="snapshot"} 0

If we could add a filesystem label, we could build easy statistics of snapshots for each filesystem:

zfs_dataset_logical_used_bytes{name="zrepl_20220407_154137_000",filesystem="rpool/application",pool="rpool",type="snapshot"} 0

I think this would add a clear benefit, and also is consistent of how we handle pool for for example.