Feature Request: Handle supports for the External Groups endpoints

[jbenaventem]

Description of the issue:

I am proposing the implementation of enterprise endpoints to manage and support external groups from an Identity Provider (IDP) within a GitHub Enterprise account. This feature would enhance the functionality of the GitHub API library by providing additional support for enterprise-level operations.

The relevant documentation can be found here: GitHub Enterprise Cloud Documentation

If there is agreement on the value of this feature, I am willing to contribute to its implementation. I believe this addition would greatly enhance the library's capabilities and provide valuable tools for managing GitHub Enterprise accounts. Thank you for considering this proposal. I am open to discussing other potential solutions for these enterprise-associated endpoints.

Regards

[bitwiseman]

PRs welcome. You might want need to do some work to get the test coverage needed in CI.

[mestebangutierrez]

@bitwiseman, I just opened a PR for solving this issue.

Please, let me know if anything else is required to let the PR go through the contribution funnel.