[4.x] Added LinkedIn OpenID Support

[joelbutcher]

This pull request add's a new provider to support LinkedIn's OpenID authentication mechanics.

resolves #284

[what-the-diff]

PR Summary

• Integration of LinkedIn OpenID Support
  The PR includes the integration of LinkedIn OpenID, which allows users to simplify the registration and login process using their LinkedIn credentials. This feature is added to both back-end PHP classes and front-end Vue components.

• LinkedIn OpenID Test Cases
  Along with the new feature, test cases for LinkedIn OpenID have also been added. These help ensure that the new feature works as expected. The test cases are added in SocialstreamRegistrationTest.php, SocialstreamAccountTest.php, and a new method in ProvidersTest.php.

• Deprecation Warning on Twitter Support
  A deprecation warning has been included in the hasTwitterSupport() method, suggesting users should switch to hasTwitterOAuth1Support() instead. This modification is to prepare users for future changes where OAuth 1.0 may be discontinued.

• Changes in Front-end Components
  To accommodate the new LinkedIn OpenID feature, necessary changes have been made to the front-end components. Particularly, a new section in ConnectedAccount.vue and modifications in the connected-account.blade.php and socialstream.blade.php files have been made.

• Changes in Existing Methods
  configureRefreshTokenResolvers() method in the SocialstreamServiceProvider class has been modified to incorporate the new LinkedIn Openid and Twitter OAuth2 providers. This ensures that these providers also support the token refresh process for extended sessions.

• Added New Laravel Package
  The laravel/socialite dependency package has been updated in the composer.json file with a specified version, needed to support the LinkedIn OpenID sign-in feature.