feat(gateway): allow localhost http:// DoH resolvers

[lidel]

This PR allows people to run own DNS over HTTP(S) resolver on the same box (localhost) without setting up unnecessary TLS certs.

Main use case is to simplify self-hosting of non-ICANN DNS systems such as ENS resolver (https://github.com/ethlimo/limo-web3-dns) by gateway operators who don't want to trust third-party DNS resolvers.

• relax https://github.com/libp2p/go-doh-resolver/blob/f2e25860684789200e3a3a911dc9a74d01771d5b/resolver.go#L55
• [ ] relax https://github.com/multiformats/go-multiaddr-dns (if needed) (doesn't appear to be needed)
• test end-to-end with localhost resolver

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 60.55%. Comparing base (08526ad) to head (df49e98).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
gateway/dns.go	0.00%	1 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #645      +/-   ##
==========================================
+ Coverage   60.50%   60.55%   +0.04%     
==========================================
  Files         245      245              
  Lines       31133    31133              
==========================================
+ Hits        18838    18852      +14     
+ Misses      10621    10607      -14     
  Partials     1674     1674              

Files with missing lines	Coverage Δ
gateway/dns.go	60.00% <0.00%> (+22.22%)	⬆️

... and 8 files with indirect coverage changes

[aschmahmann]

Main use case is to simplify self-hosting of ENS resolves by gateway operations etc.

This PR works and for tools like CoreDNS that support DNS over HTTP (and not just HTTPS) this might be enough. If there's not enough support here folks might end up asking us for DNS over UDP / TCP support, but we can tackle that as the need arises.

For what it's worth a nice thing about pushing on DNS-over-HTTP is that it makes it easier for folks who want to self-host while also using web-browsers since UDP/TCP are not available to javascript in browsers. For some cases like ENS this might not be a big deal since they can wrap the Ethereum JSON-RPC, but it might matter for other name systems.

[aschmahmann]

Updated the comment above given that CoreDNS does support DNS-over-HTTP in addition to DNS-over-HTTPS.

FYI CoreDNS (and therefore the CoreDNS ENS resolver) supports DNS-over-HTTP, although the UX for this is that you configure listening on "https://" rather than "http://" and just not pass a certificate (which is what tripped me up initially 😅).

I think we should be good to go on a merge here, pending reviews.

[lidel]

@aschmahmann thank you for adding tests and libp2p/go-doh-resolver#28. Lgtm.

I've reviewed libp2p/go-doh-resolver#28, limited it to localhost, merged, released, and switched this PR to go-doh-resolver v0.5.0.

Merging as it cleans up go.mod as bit as well.