chore(dns): remove empty dns port completely

[Icarus9913]

Refer to #8640, we have drop usage of empty dns port carefully and left some properties for rollback/downgrade. Nowadays, we gonna remove it completely.

close #8639

Elaboration

• What does EmptyDNSPort do?

Refer to the first PR generate DNS filter, we introduced Envoy DNS filter. But at that time, there was no way to disable upstream resolvers in DNSFilter thus we used the coreDNS Empty DNS port as a dummy resolver to respond the empty response.
Later we found Users can disable external DNS resolution by omitting the client configuration object. from https://www.envoyproxy.io/docs/envoy/latest/configuration/listeners/udp_filters/dns_filter , which corresponds to the previous PR source codes change https://github.com/kumahq/kuma/pull/8640/files#diff-4188e1209c75b5064ff4c5f6b33180cb84e164a99021efa1fa01d2938e06e1f1L55-L80

• Why didn't we drop it completely by chore(dns): drop usage of empty dns port #8640 ?

Due to the first PR codes https://github.com/kumahq/kuma/pull/1807/files#diff-4cf14047d8fdc54a2debb5bfa2b95f2f5cccc7d48d7803cf3700ff2934ad86cbR23-R25 , it would not generate the configurations

	if dnsPort == 0 || emptyDnsPort == 0 {
		return nil, nil
	}

If we totally removed the EmptyDNSPort from the previous PR #8640 and the user downgrade to a earlier CP version, the user must meet the if condition and return nil empty configuration which leads to interruption in the traffic.

Checklist prior to review

• Link to relevant issue as well as docs and UI issues --
• This will not break child repos: it doesn't hardcode values (.e.g "kumahq" as a image registry) and it will work on Windows, system specific functions like syscall.Mkfifo have equivalent implementation on the other OS --
• Tests (Unit test, E2E tests, manual test on universal and k8s) --
  • Don't forget ci/ labels to run additional/fewer tests
• Do you need to update UPGRADE.md? --
• Does it need to be backported according to the backporting policy? (this GH action will add "backport" label based on these file globs, if you want to prevent it from adding the "backport" label use no-backport-autolabel label) --

[Icarus9913]

cc @jakubdyszkiewicz