Feature request: expose the upstream DNS ports to be configurable

[mix3d]

Was considering using this but found some inconsistencies with the documentation and what is hardcoded.

DoH "uses cloudflare (1.1.1.1 / 1.0.0.1) by default" is different than "is hardcoded to", even though cloudflared supports pointing to any DNS service.

Apart from cloning and modifying the source myself to different DoH endpoints, what would it take to reconfigure this to expose the DNS IPs as part of the root level options? (For example I'm currently using the "family-friendly" 1.1.1.3 service instead)

Thanks!