Add timestamp to btrfs storage snapshot overview and detail

[2nv2u]

Page: Storage

As requested to make this a feature request, it would be great to have a timestamp added to the new snapshots view for the btrfs partitions in the storage plugin:

#20234

This can be retrieved fomr the metadata from the snapshots themselves: btrfs subvol show {snapshot}

[jelly]

We don't have this data readily available from UDisks or from btrfs subvolume list, so implementing this more properly needs some more structural work:

Usually snapshots are already conveniently named but if they aren't showing the Creation date (which I assume is what you asked for) is useful.

[jelle@t14s][~/projects/cockpit/test-logout-account-dialog]%sudo btrfs subvolume show /.snapshots/26-02-2024
snapshots/26-02-2024
        Name:                   26-02-2024
        Received UUID:          -
        Creation time:          2024-02-26 10:17:04 +0100