fix(dns): disable new dns client by default

[chobits]

Summary

For the ongoing 3.8 release, we need to disable the new DNS client by default to avoid breaking the original DNS client's behavior.

Dont merge it until 3.8 RC2, 3.8 RC1 still enables the new DNS client for testing.

Checklist

• The Pull Request has tests (using original test cases)
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

Fix KAG-5174

[chobits]

Dont merge it until 3.8 RC2, 3.8 RC1 still enables the new DNS client for testing.
pr/ready (but hold merge) flag

[team-gateway-bot]

Successfully created cherry-pick PR for master:

• https://github.com/kong/kong-ee/pull/10015

[team-gateway-bot]

Successfully created backport PR for release/3.8.x:

• [backport -> release/3.8.x] fix(dns): disable new dns client by default #13525