rework H3 ALPN handling

[marten-seemann]

Fixes #2089.

[codecov-io]

Codecov Report

Merging #2090 into master will decrease coverage by <.01%.
The diff coverage is 68.42%.

@@            Coverage Diff             @@
##           master    #2090      +/-   ##
==========================================
- Coverage   85.44%   85.43%   -<.01%     
==========================================
  Files          98       98              
  Lines        7271     7276       +5     
==========================================
+ Hits         6212     6216       +4     
  Misses        775      775              
- Partials      284      285       +1

Impacted Files	Coverage Δ
http3/client.go	85% <100%> (+0.15%)	⬆️
http3/server.go	53.24% <62.5%> (+0.41%)	⬆️

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[mholt]

Oooo I didn't see this until just now, can't wait to try this out first thing in the morning!

[mholt]

It works!

You can view the current integration at caddyserver/caddy#2727. It's still a PoC/WIP of course.

[marten-seemann]

@mholt Cool, thanks for testing this! Super excited to see this in Caddy soon.