Attractor interface config to support IP ranges

[zolug]

Supporting multiple Trenches (Attractors) sharing the same VLAN network requires some coordination when it comes to assigning IPs to external interfaces of FEs (to avoid duplicated IPs).

Describe the solution you'd like
One possible way doing so is to split the IP network into IP ranges and distribute said ranges between the respective Attractors.

It requires changes in the Remote VLAN NSE to support IP ranges as well: networkservicemesh/cmd-nse-remote-vlan#110

Describe alternatives you've considered
A centralized NSE that would serve multiple Attractors based on some shared property (like e.g. VLAN ID and network) could work as well in theory. But It would require major changes. And it would be hard or almost impossible to coordinate independent Meridio installations.