extend provider options with httpClientConfig key

[sandacn]

We can pass options such as timeout proxy to Provider in options, such as

$provider = new \League\OAuth2\Client\Provider\GenericProvider([
    'clientId'                => 'XXXXXX',    // The client ID assigned to you by the provider
    'clientSecret'            => 'XXXXXX',    // The client password assigned to you by the provider
    'redirectUri'             => 'http://my.example.com/your-redirect-url/',
    'urlAuthorize'            => 'http://service.example.com/authorize',
    'urlAccessToken'          => 'http://service.example.com/token',
    'urlResourceOwnerDetails' => 'http://service.example.com/resource',
    'proxy'                   => '192.168.0.1:8888',
    'verify'                  => false
]);

But it is not extensible when need to pass more http client config parameters.
I made a change which add special key for this situation.

$provider = new \League\OAuth2\Client\Provider\GenericProvider([
    'clientId'                => 'XXXXXX',    // The client ID assigned to you by the provider
    'clientSecret'            => 'XXXXXX',    // The client password assigned to you by the provider
    'redirectUri'             => 'http://my.example.com/your-redirect-url/',
    'urlAuthorize'            => 'http://service.example.com/authorize',
    'urlAccessToken'          => 'http://service.example.com/token',
    'urlResourceOwnerDetails' => 'http://service.example.com/resource',
    'httpClientConfig' => [
        'proxy'                   => '192.168.0.1:8888',
        'verify'                  => false
    ],
]);

This becomes more clear and extensible.

The key name: httpClientConfig, use the guzzle 's client construct parameter, the name is config.
So the key name: httpClientConfig.

If user use the httpClientConfig for option, the option will be override by the httpClientConfig. In test cases, these is a case for this:

        $configTimeout = 20;
        $optionsTimeout = 10;
        $httpClientConfig = [
            'timeout' => $configTimeout,
        ];
        $options = [
            'timeout' => $optionsTimeout,
            'httpClientConfig' => $httpClientConfig,
        ];
        $mockProvider = new MockProvider($options);

        $config = $mockProvider->getHttpClient()->getConfig();

        $this->assertContains('timeout', $config);
        $this->assertEquals($configTimeout, $config['timeout']);

Finally this patch is compatible with previous version.

Thanks.

[codecov]

Codecov Report

Merging #771 (1f5dcb6) into master (77def43) will not change coverage.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##              master      #771   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
- Complexity       180       182    +2     
===========================================
  Files             20        20           
  Lines            464       466    +2     
===========================================
+ Hits             464       466    +2     

Impacted Files	Coverage Δ
src/Provider/AbstractProvider.php	100.00% <100.00%> (ø)
src/Tool/RequestFactory.php	100.00% <0.00%> (ø)