Feature: Added support for logging in/out of GitHub

[yaira2]

Resolved / Related Issues

• Were these changes approved in an issue or discussion with the project maintainers? In order to prevent extra work, feature requests and changes to the codebase must be approved before the pull request will be reviewed. This prevents extra work for the contributors and maintainers.
  Closes Feature: Switch git account and log out #13049...

Validation
How did you test these changes?

• Did you build the app and test your changes?
• Did you check for accessibility? You can use Accessibility Insights for this.
• Did you remove any strings from the en-us resource file?
  • Did you search the solution to see if the string is still being used?
• Did you implement any design changes to an existing feature?
  • Was this change approved?
• Are there any other steps that were used to validate these changes?
  1. Push commit from the stable version of Files to grant GitHub access
  2. Checkout this branch and navigate to settings, there should be a new settings page for "Git".
  3. Confirm the logout button removes the credentials and that the login button becomes visible
  4. Confirm the login button opens the authentication prompt

Screenshots (optional)
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