Add text/uri-list attachment samples

[davidjgoss]

🤔 What's changed?

Adds a scenario and corresponding step definition for doing a "link" attachment.

⚡️ What's your motivation?

See cucumber/common#2191

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

📋 Checklist:

• Merge and release Add support for link attachments fake-cucumber#121 so we have the new link method here
• 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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