This includes Websocket over HTTP/3.

Since quicer, which provides the QUIC implementation,
is a NIF, Cowboy cannot depend directly on it. In order
to enable QUIC and HTTP/3, users have to set the
COWBOY_QUICER environment variable:

  export COWBOY_QUICER=1

In order to run the test suites, the same must be done
for Gun:

  export GUN_QUICER=1

HTTP/3 support is currently not available on Windows
due to compilation issues of quicer which have yet to
be looked at or resolved.

HTTP/3 support is also unavailable on the upcoming
OTP-27 due to compilation errors in quicer dependencies.
Once resolved HTTP/3 should work on OTP-27.

Because of how QUIC currently works, it's possible
that streams that get reset after sending a response
do not receive that response. The test suite was
modified to accomodate for that. A future extension
to QUIC will allow us to gracefully reset streams.

This also updates Erlang.mk.

Original fix by Ali Farhadi <a.farhadi@gmail.com>.

To avoid having the connection get closed due to us taking
too long on unreliable environments like GitHub Actions.

This is caused by the timeout being 1s after the period.
When the CI environment is overloaded, sometimes the
timeout will trigger. We retry, knowing that the
timetrap will catch us if we retry too much.

GitHub Actions runners are not as good as self-hosted BuildKite
so some adjustments need to be made to timeouts and such.

This allows conditionally generating an etag.