Added support to configure the Oauth2 access token location in requests

[rhertogh]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	❌
Fixed issues	#386

This PR adds support for easy configuration of the location of the access token in API requests for Oauth 2 clients.
It also adds a "plain" oauth 2 client that uses the access token in the header by default as specified in RFC6749#section-7.

[what-the-diff]

PR Summary

• Introduction of Access Token Locations for OAuth classes
  This PR introduces two new constants ACCESS_TOKEN_LOCATION_HEADER and ACCESS_TOKEN_LOCATION_BODY to each of the OAuth2.php, OpenIdConnect.php, GitHub.php, and TwitterOAuth2.php files. In result, this eases the configuration of where access tokens are placed in API requests, adding versatility to our access management.

• Property Addition to OAuth classes
  A new property $accessTokenLocation has been added to the OAuth2.php and OpenIdConnect.php files. This feature enhances the ability to configure where the access token will be placed in API requests.

• New OAuth2 Client
  The addition of a new file Oauth2Client.php will help manage OAuth2 authentication flow more effectively.

• Unit Test Additions for Improved Robustness
  New test files for a variety of modules (FacebookTest.php, GitHubTest.php, GoogleHybridTest.php, GoogleTest.php, LinkedInTest.php, LiveTest.php, Oauth2ClientTest.php, OpenIdConnectTest.php, TwitterOAuth2Test.php, VKontakteTest.php, YandexTest.php) were added, enhancing the overall testing coverage. This measure ensures each module is functioning as expected and can prevent unwanted future bugs.

• New Base Client Test Case
  A base test file BaseOauth2ClientTestCase.php has been added and includes methods that standardize OAuth2 client operations for testing: createClient(), getExpectedTokenLocation(), getAccessTokenHeaderTypeName(), getAccessTokenBodyParamName(), and testTokenLocation(). These additions should facilitate smoother, more consistent testing across all OAuth2 clients.

[samdark]

Thank you.