ref(derp): Default DNS name rooted at the DNS root

[flub]

Description

This makes sure that the default DNS name starts at the DNS root so
that DNS resolvers do not start searching their search domains.

Notes & open questions

Change checklist

• Self-review.
• Documentation updates if relevant.
• Tests if relevant.

[dignifiedquire]

Does this work in all cases? we also do http requests to this URL

[flub]

Yes, that works. HTTP just does DNS under the hood like anyone else. Also, tests pass :)

[divagant-martian]

this means the constant can be used in at least one more place I think: ah it's not exactly the same, this is what I had in mind

iroh/iroh-net/src/hp/netcheck.rs

Line 896 in a0ae228

let stun_servers = vec![("https://derp.iroh.network.", DEFAULT_DERP_STUN_PORT)];

[dignifiedquire]

@flub merge conflicts