Set FORCE_COLOR based on deprecated format option

[davidjgoss]

🤔 What's changed?

When we detect a value has been set (either true or false) for the colorsEnabled format option, set the FORCE_COLOR environment variable to the corresponding value.

⚡️ What's your motivation?

We're moving away from this custom option and leaning into the pseudo-standard environment variable. This is an intermediate step before we remove the option entirely, so existing usages will cause the environment variable to be set, and all formatters will still work as expected.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)
• 💥 Breaking change (incompatible changes to the API)

📋 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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