export IConfiguration interface for API users

[davidjgoss]

🤔 What's changed?

Export IConfiguration on the API entry point.

⚡️ What's your motivation?

So API users can type the configuration objects they compose and pass in to the loadConfiguration function. I'm doing this now and it's painful without the typing.

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

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[coveralls]

Coverage remained the same at 98.297% when pulling 4527494 on fix/export-configuration-interface into 0f5dab7 on main.