feat: experimental HTTP/3 support + optional HTTP/2 disabling

[buchdag]

@SchoNie I went the extra mile and opened a draft PR with what I got so far. It seems mostly functional to me, let me know if you think something is missing / should be done differently.

It indeed work when replacing proxy_set_header Host $http_host; with proxy_set_header Host $host;, should we also replace the other uses of $http_host beside this one ?

The PR still lacks documentation at this point, and I don't think it can be automatically tested beside parsing the rendered template (Python's request is not even capable of doing HTTP/2).

New labels on the proxied containers:

• com.github.nginx-proxy.nginx-proxy.http2.enable:
  enable HTTP/2 support when set to true (default: true)
• com.github.nginx-proxy.nginx-proxy.http3.enable:
  enable HTTP/3 support when set to true (default: false)

New environment variables on the proxy container:

• ENABLE_HTTP2: globally enable HTTP/2 when set to true (default: true)
• ENABLE_HTTP3: globally enable HTTP/3 when set to true (default: false)

closes #2170
closes #1055

[SchoNie]

I think it is safe to change to $host there is only 1 instance left in the $http_x_forwarded_proto map.
I ran the tests with change and do not encounter any difference.

[buchdag]

I re-organised the template a bit so that HTTP/3 related stuff is a bit more grouped together.

More importantly I moved the add-header statement for Alt-Svc from the location template to the server block to avoid overriding the HSTS header (thanks @Knapoc for spotting this in #2271).

I also removed the $http3 variable from logs because as explained in discussion above we already have the protocol logged through the $request variable.

And finally I replaced the last $http_host instance with $host.

[buchdag]

@SchoNie @Knapoc is it okay if I add you as co-authors on relevant commits ?

[SchoNie]

👍
I did create a few tests. I adjusted the hsts test to check for overridden headers.
And made soms basic http3 tests. Mostly to check for config syntax as there is not really a method to test by requests.

Will try to push later when at office and then you can improve or discard😅

cool this PR is getting along! Hopefully it helps more people to enable QUIC and maybe it encourages to use of this project as a early adopter.

[SchoNie]

HSTS override tests, http2 & http3 tests: SchoNie@618da60
Feel free to use, improve or discard.

[buchdag]

@SchoNie sorry for the lack of activity on august, the tests looked interesting, do you still have them ?

[SchoNie]

@buchdag Yes. Still have the tests: 27cc611