Support for automatically updating credentials from Third-Party SAML Solution Providers

As a user of the AWS CLI, I would like aws-shell to automatically update my credentials from a third-party SAML provider (like Okta). This will save time from running a separate script every time my temporary credentials expire (like what happens in this [blog post](https://blogs.aws.amazon.com/security/post/Tx1LDN0UBGJJ26Q/How-to-Implement-Federated-API-and-CLI-Access-Using-SAML-2-0-and-AD-FS)). Here is an example from someone who attempts to solve the problem - https://github.com/nshobayo/AWS-CLI

It would be nice to to have incorporate the features from that project and incorporate them here. I would be okay if I had to be prompted re-enter my SSO credentials every 4 hours if that's possible. With this feature, it would make it easier for those that want to integrate Third-Party SAML Solution Providers, but also want make it easy for developers to still use the AWS CLI.