Add CLI option to enable dot1q encap on the interface resource

[hellt]

To allow selecting the encap type of the interface we need to add a cli option to either create the untagged or dot1q capable interfaces.

--edge-encapsulation can be a flag name with value dot1q for setting up the tag support

[FloSch62]

@hellt do you want that only for edge interfaces or also for isl interfaces?

[hellt]

We can start with edge only for now. But if it's easy we can add a flag for isl encap

[FloSch62]

closed by #120