feat(core): Add fork functionality

[hminaee-tc]

Describe the need

The current GitHub Terraform provider does not support forking repositories via configuration. This functionality would be valuable for teams or individuals who want to create forks of repositories as part of their infrastructure-as-code workflows.

What do you want to happen?
I would like to introduce a new resource (e.g., github_repository_fork) or an extension of the existing repository resource that allows users to define and manage repository forks directly from Terraform.

SDK Version

No response

API Version

No response

Relevant log output

N/A — this is a new feature request and not related to an error or failure.

Code of Conduct

• I agree to follow this project's Code of Conduct

Note

I already created PR for this feature and it is ready for review
#2678

[hminaee-tc]

Please note I am working on the changes and soon will create a related PR for this requested feature

[hminaee-tc]

The PR for this feature is created and ready for review
#2678

@nickfloyd Just FYI I updated the PR link (I created a different branch name to main just to avoid confusion)
Please use the posted PR url above for this issue
Thanks