Add CHANGELOG_PENDING.md for AWS SSO Credential Provider
### SDK Features
+* `aws/credentials/ssocreds`: Add support for AWS Single Sign-On (SSO) Credential Provider ([#3755](https://github.com/aws/aws-sdk-go/pull/3755))
+* `aws/session`: Support has been added to resolve shared configuration profiles that are configured for AWS Single Sign-On (SSO) ([#3755](https://github.com/aws/aws-sdk-go/pull/3755))
### SDK Enhancements
