chore: Extract functions and add test coverage

[zkoppert]

Pull Request

Extract functions from code in main() and add test coverage for the new functions. This doesn't extract all functionality from the main() but its a start. Follow up PR's possible but not required given current usage of this action.

Proposed Changes

This pull request refactors the open_contrib_pr.py script to improve code organization and adds new test cases for better coverage. The most important changes include extracting functions for cloning repositories and creating pull requests, updating the main logic to use these functions, and adding comprehensive unit tests for the new functions and existing authentication logic.

Readiness Checklist

Author/Contributor

• If documentation is needed for this change, has that been included in this pull request
• run make lint and fix any issues that you have introduced
• run make test and ensure you have test coverage for the lines you are introducing
• If publishing new data to the public (scorecards, security scan results, code quality results, live dashboards, etc.), please request review from @jeffrey-luszcz

Reviewer

• Label as either bug, documentation, enhancement, infrastructure, maintenance or breaking

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