2.0.0 Release (#58)

* Automated commit message

* Automated commit message

* add changelog

---------

Co-authored-by: PayPalServerSDKs <server-sdks@paypal.com>

doc/auth/oauth-2-client-credentials-grant.md

@@ -27,6 +27,9 @@ Documentation for accessing and setting credentials for Oauth2.
 You must initialize the client with *OAuth 2.0 Client Credentials Grant* credentials as shown in the following code snippet. This will fetch the OAuth token automatically when any of the endpoints, requiring *OAuth 2.0 Client Credentials Grant* authentication, are called.
 
 ```php
+use PaypalServerSdkLib\Authentication\ClientCredentialsAuthCredentialsBuilder;
+use PaypalServerSdkLib\PaypalServerSdkClientBuilder;
+
 $client = PaypalServerSdkClientBuilder::init()
     ->clientCredentialsAuthCredentials(
         ClientCredentialsAuthCredentialsBuilder::init(
@@ -46,6 +49,9 @@ Your application can also manually provide an OAuthToken using the setter `oAuth
 Whenever the OAuth Token gets updated, the provided callback implementation will be executed. For instance, you may use it to store your access token whenever it gets updated.
 
 ```php
+use PaypalServerSdkLib\Authentication\ClientCredentialsAuthCredentialsBuilder;
+use PaypalServerSdkLib\PaypalServerSdkClientBuilder;
+
 $client = PaypalServerSdkClientBuilder::init()
     ->clientCredentialsAuthCredentials(
         ClientCredentialsAuthCredentialsBuilder::init(
@@ -68,6 +74,9 @@ $client = PaypalServerSdkClientBuilder::init()
 To authorize a client using a stored access token, set up the `oAuthTokenProvider` in `ClientCredentialsAuthCredentialsBuilder` along with the other auth parameters before creating the client:
 
 ```php
+use PaypalServerSdkLib\Authentication\ClientCredentialsAuthCredentialsBuilder;
+use PaypalServerSdkLib\PaypalServerSdkClientBuilder;
+
 $client = PaypalServerSdkClientBuilder::init()
     ->clientCredentialsAuthCredentials(
         ClientCredentialsAuthCredentialsBuilder::init(