Enhance "launch-blueprint" to allow passing Github Username and Token to enable import from private repositories

## Describe your feature request

Can we enhance the "[launch-blueprint](https://github.com/aws/codecatalyst-blueprints/blob/main/packages/blueprints/launch-blueprint/src/blueprint.ts)" to allow passing Github Username and Token to enable import from private repositories?

This could potentially be two input fields (optional) that the user can enter when going through the wizard

## Additional context

This will allow users to import source code from private github repositories

Start with packages/blueprints/launch-blueprint/src/blueprint.ts and trace how the wizard currently gathers inputs and imports source code. Determine how optional GitHub username and token inputs should support private repositories, including the expected completion behavior, then verify the private-repository import flow.

Written by the indexing model from the issue text.