[curl] Add http3 support via the nghttp3+openssl backend

[MichalPetryka]

Is your feature request related to a problem? Please describe.

Curl has added experimental support for enabling http3 support with just nghttp3+OpenSSL without the use of other OpenSSL forks which have been deemed unsuitable for vcpkg before as per #32109 (comment).
As such, vcpkg can now add a feature exposing support for it so that users can use curl to communicate with http3 servers.

Proposed solution

Expose an http3 feature using the nghttp3+OpenSSL backend.

Describe alternatives you've considered

No response

Additional context

I've noticed that enabling the http2 feature enables the SChannel SSL backend on Windows today, this is an issue since http3 support in Curl is exclusive with Multi-SSL support so http3 would somehow need to force disable that.