Add models for VLAN, VNI, VTEP, VLAN-VNI mappings, and EVPN instances. Supports L2VNI and L3VNI types for EVPN-VXLAN fabric. Ref: #41
Add core infrastructure models for Device, Interface, IPAddress, and Platform based on the arista-evpn-vxlan-clab topology. Ref: #41