Add per-port domain override

[es3n1n]

this pr adds a new domain field to PortSpec that lets each port override its dns subdomain prefix (port.Domain + "." + domainName instead of the default {challengeName}-web.{domainName} or {challengeName}.{domainName})

also fixes the NodePort service deduplication to check the resolved service port instead of the raw port.Port field (please let me know if you want this to be in a separate pr)

(external-dns.go was edited by go fmt during make build so I assumed it will be fine if i attach it to this pr)

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