Add extra_probe_peers serialization, add Nautilus test JSON

[0X1A]

- This field may have been missed in previous versions as the
json test files in `tests` did not have this field populated.
Looking at older Ceph versions the struct `entity_addr_t` has
not changed significantly enough that would break backward
compatibility should the `extra_probe_peers` field be populated

[cholcombe973]

I assume you've tested this against older versions? It certainly seems reasonable

[0X1A]

This repo contains JSON from the same monitor commands across other versions. Outside of that, I haven't done any additional testing. We would have to get some cluster up that have those fields available in their JSON