fix(dns): allow http:// DoH resolvers

[lidel]

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

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

• relax https://github.com/libp2p/go-doh-resolver/blob/f2e25860684789200e3a3a911dc9a74d01771d5b/resolver.go#L55
• relax https://github.com/multiformats/go-multiaddr-dns (if 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 59.87%. Comparing base (0190b70) to head (f736895).
Report is 73 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   59.75%   59.87%   +0.12%     
==========================================
  Files         238      238              
  Lines       29999    29999              
==========================================
+ Hits        17926    17963      +37     
+ Misses      10450    10418      -32     
+ Partials     1623     1618       -5     

Files with missing lines	Coverage Δ
gateway/dns.go	37.77% <0.00%> (ø)

... and 13 files with indirect coverage changes

[aschmahmann]

I don't think this is going to be enough:
https://github.com/libp2p/go-doh-resolver/blob/f2e25860684789200e3a3a911dc9a74d01771d5b/resolver.go#L55

Note: AFAICT there is no DNS-over-HTTP spec for some reason it's specified as being over HTTPS, however I definitely see your point and have definitely felt the pain over the self-signed cert dance just to run local resolvers

[lidel]

Yep, filled this PR because I am looking at https://github.com/libp2p/go-doh-resolver and https://github.com/multiformats/go-multiaddr-dns to wire up TTL (to fix #329 (comment) for DNSLinks), so likely will relax things there as well, and get back to this PR draft.