Replace Guzzle by Symfony HttpClient #2

Transform hapiclient-php-guzzle7 into hapiclient-symfony.

HapiClient\Http\HapiClient.php

• Replace usage GuzzleHttp\Client by Symfony\Contracts\HttpClient\HttpClientInterface
• Remove usage of \GuzzleHttp\Psr7\Request, use HapiClient\Http\Request ( no need of \GuzzleHttp\Psr7\Utils::streamFor($body) as HttpClient already streams the body)

Bonus

Find a replacement for GuzzleHttp\UriTemplate\UriTemplate