[feature] support round-robin DNS

[dreamer2q]

Many DNS providers, like Cloudflare DNS support round-robin DNS.

What is round-robin DNS?

• https://www.cloudflare.com/zh-cn/learning/dns/glossary/round-robin-dns/

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I haven't seen any documentations about configuring this feature. It seems that godns can only bind one address for a specified domain/subdomain ?

In my view, this feature helps when you have more than one public addresses. Unfortunately I am one of them who has more than one ips. I just want this feature to make my internet more smooth even if one of my ips is dowm.