[gen] add automatic IPv6 generation (fixes #11613)

data/grid5000/grid5000.json

...grid5000/sites/grenoble/clusters/troll/nodes/troll-1.json

...grid5000/sites/grenoble/clusters/troll/nodes/troll-2.json

...grid5000/sites/grenoble/clusters/troll/nodes/troll-3.json

...grid5000/sites/grenoble/clusters/troll/nodes/troll-4.json

data/grid5000/sites/nancy/clusters/grue/nodes/grue-1.json

data/grid5000/sites/nancy/clusters/grue/nodes/grue-2.json

data/grid5000/sites/nancy/clusters/grue/nodes/grue-3.json

data/grid5000/sites/nancy/clusters/grue/nodes/grue-4.json

data/grid5000/sites/nancy/clusters/grue/nodes/grue-5.json

input/grid5000/ipv6.yaml

.../grid5000/sites/grenoble/clusters/dahu/dahu_ipv6.yaml.erb

...rid5000/sites/grenoble/clusters/troll/troll_ipv6.yaml.erb

.../grid5000/sites/grenoble/clusters/yeti/yeti_ipv6.yaml.erb

...id5000/sites/lille/clusters/chetemi/chetemi_ipv6.yaml.erb

...id5000/sites/lille/clusters/chiclet/chiclet_ipv6.yaml.erb

...5000/sites/lille/clusters/chifflet/chifflet_ipv6.yaml.erb

...5000/sites/lille/clusters/chifflot/chifflot_ipv6.yaml.erb

...0/sites/luxembourg/clusters/granduc/granduc_ipv6.yaml.erb

...luxembourg/clusters/petitprince/petitprince_ipv6.yaml.erb