[Feature]: Image - Add migration documentation for center-contain and center-cover fit modes

[spenoff]

Area

React Components (@fluentui/react-components)

Describe the feature that you would like added

The v8 Image component's ImageFit enum included centerContain and centerCover values that have no direct equivalent in the v9 Image component. The migration documentation does not mention these values or provide guidance on how to achieve equivalent behavior.

Proposed solution: Update the v8 → v9 migration guide for the Image component to:

• Document how centerContain and centerCover map (or don't map) to v9
• Provide CSS-based workaround examples using object-fit + object-position

Additional context

No response

Have you discussed this feature with our team

mainframev

Validations

• Check that there isn't already an issue that requests the same feature to avoid creating a duplicate.

Priority

Low