bcachefs support

[hgkamath]

Filing this bug to track support for bcachefs partitions, volumes, subvolumes and cache devices

blivet and blivet-gui are used as the installation partition manager in distributions such as Fedora.
bcachefs support will let the user to use the gui partitioning tool for such without having to go to command line and invoke commands directly.

• corresponding issue in blivet-gui project bcachefs support blivet-gui#439

[vojtechtrefny]

We are definitely planning to support bcachefs in the future, but we currently don't have any concrete plans or timeline for it. We'll need to start with libblockdev support, some initial work was already started, see storaged-project/libblockdev#959