add flag for init --repo with github personal access token

[purplecabbage]

This enables quickstarts in private repos

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] I have signed the Adobe Open Source CLA.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8c5d879) 100.00% compared to head (bdcd7b0) 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #746 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 56 56 Lines 3231 3232 +1 Branches 611 612 +1 ========================================= + Hits 3231 3232 +1 ```

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