feat: add subdomain/hostname to pods created

[PFC-developer]

This PR adds hostname & subdomain to pods on creation (similar to how stateful sets do).
This is needed for a headless service to have podname.servicename... DNS resolution (instead of just servicename).
ala
`
root@harpoon-horcrux-1:/# host harpoon-0.harpoon
harpoon-0.harpoon.cosmos.svc.cluster.local has address 10.0.9.240

root@harpoon-horcrux-1:/# host harpoon-1.harpoon
harpoon-1.harpoon.cosmos.svc.cluster.local has address 10.0.7.151

root@harpoon-horcrux-1:/# host harpoon-2.harpoon
harpoon-2.harpoon.cosmos.svc.cluster.local has address 10.0.8.192

root@harpoon-horcrux-1:/# host harpoon
harpoon.cosmos.svc.cluster.local has address 10.0.7.151
harpoon.cosmos.svc.cluster.local has address 10.0.9.240
harpoon.cosmos.svc.cluster.local has address 10.0.8.192
`
before this patch only the last 'DNS' lookup would work.
I don't believe it has any negative effects

[DavidNix]

This is great, thank you.

All changes require unit test coverage before merge. See CONTRIBUTING.md. Please look at pod_builder_test.go and add tests there.

[PFC-developer]

moved logic to pod_builder and added test.

[PFC-developer]

changes applied

[DavidNix]

Thanks!