[Bug]: Cannot use subdomain as DNS search domain

[lilotter45]

🐛 Describe the Bug

When attempting to add a subdomain (e.g. zt.my.tld) as the search domain for DNS, the error "Invalid DNS domain provided" is returned.

🔍 Steps to Reproduce

In the network configuration screen (have only tried this for a network that is part of an organization):

• Expand the DNS configuration
• Enter any subdomain, e.g. zt.example.com and a valid IP address
• Click SUBMIT

🔧 Deployment Type

• Docker
• Standalone

✨ Expected Behavior

Users should be able to use a subdomain as the search domain for DNS. This is supported in Zerotier's management UI and is used as the example in this comment on search domains in this repo.

📋 ZTNET Logs

N/A

🖼 Screenshots

No response