Add authentication support for WireMock Cloud (wiremock.io)

[lstrojny]

Enables wiremock-php to work with wiremock.io without breaking backwards compatibility. This is how it works:

$curl = new Curl(new TokenAuthenticator($token));
$client = new WireMock(new HttpWait($curl), $curl, SerializerFactory::default(), $host, 443, 'https');