fix(modeldetailspreparationdetails): match ML Requirements

[lprovost-coveo]

Acceptance Criteria

After introduction it was discovered that this property has a typo. It is gramatically incorrect but the current value is indeed facetsDetails and not facetDetails.

The property has a high cost and impact to rename so the Service team won't rename it anytime soon. To make things work we need to match their property name.

https://github.com/coveo-platform/ml-config-service/pull/2456

• My changes are publicly available, documented, and deployed in production. (i.e. on Swagger)
• JSDoc annotates each property added in the exported interfaces
• The proposed changes are covered by unit tests
• Commits containing breaking changes a properly identified as such
• README.md is adjusted to reflect the proposed changes (if relevant)
• My merge commit message will be conventional (See Conventional Commit)

[github-actions]

🎉 This PR is included in version 57.12.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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