refactor(iroh-net): Switch to new iroh-relay route /relay instead of /derp

[matheus23]

Split out from #2419, copy of #2441, because I forgot to switch the base branch 🙃

Splitting this out means we can deploy the relay changes one release in advance to the changes in the client.

Otherwise, we'd need to update the relays ASAP when we release 0.20, as clients will expect to be able to connect to the /relay route (which may not be deployed immediately after the release).

Description

• Switches the client to connect to /relay instead of /derp.

Breaking Changes

None

Notes & open questions

Also a PR related to #2378

I allowed myself to add in another derive_more::Debug instance instead of a custom, outdated impl Debug, if that's okay with you 😁

Change checklist

• Self-review.
• Documentation updates if relevant.
• Tests if relevant.
• All breaking changes documented.

[matheus23]

Base branch didn't switch automatically in the original PR... Will need to address conflicts today ✌️

[matheus23]

This PR contains the same +5 -12 lines of code change that #2441 does (I verified this manually).

[dignifiedquire]

one issue with this I see is that relays that are not updated will not work anymore, so we might want to wait even one more release to merge this

[matheus23]

@dignifiedquire one release more seems somewhat arbitrary.
Can we tell partners that run their own relay that they have to update their relays before they update their clients?
This will be true regardless of when we release this change.

[matheus23]

K. Talked with dig. it's a social problem: We need enough time to make sure we've told everyone who runs their own relay to update their relays before they update their code. That's all.

[matheus23]

@dignifiedquire looks like you've solved the social problem, given this is now assigned the 0.21 milestone.
Can I have a quick ✅ on this PR? It's actually the same code as another PR that was already accepted.