Allow custom domain resolution settings in Flashstart UI

[cotosso]

Description
Add a section in the Flashstart UI where users can specify certain domains and define which dns servers should be used to resolve them.

Why and what for
currently, all dns queries are sent to FlashStart DN, however, in some cases, users may need to resolve specific domains using different DNS servers. this can be useful for:

• ensuring internal domains are resolved correctly
• directing queries for specific services to preferred dns providers

Proposed solution
introduce a dedicated section in the Flashstart UI that allows users to:

• Enter a list of domains
• specify which dns server(s) should handle the resolution for each domain