Add support for SSL certificate validation

[MrMage]

Currently, HTTPScheme.https creates a TLS client configuration with certificateVerification: .none. There should be an option to enable certificate validation. If that requires the user to pass in extra trust roots, those could be passed in as an extra argument, e.g. like this:

extension HTTPScheme {
    func makeHttps(certificateVerification: ..., trustRoot: ... = .default) -> HTTPScheme { ... }
}

[tanner0101]

This has been fixed in 3.1.7