Check containerlab topologies without links #41

Check if there are any containerlab topology yaml files without configured links. For example:

name: pvrst-per-vlan-rapid-spanning-tree
mgmt:
network: mgmt-ipv4
ipv4-subnet: 10.65.97.0/24
topology:
kinds:
cisco_iol:
image: docker-registry.nwl.lab/cisco_iol:17.12.01
nodes:
SW2:
kind: cisco_iol
mgmt-ipv4: 10.65.97.110
startup-config: ./clab-pvrst-per-vlan-rapid-spanning-tree/SW2/startup-config.cfg.partial
SW3:
kind: cisco_iol
mgmt-ipv4: 10.65.97.120
startup-config: ./clab-pvrst-per-vlan-rapid-spanning-tree/SW3/startup-config.cfg.partial
SW1:
kind: cisco_iol
mgmt-ipv4: 10.65.97.130
startup-config: ./clab-pvrst-per-vlan-rapid-spanning-tree/SW1/startup-config.cfg.partial
links: []