Updating Feature store classes name and operations for private preview

[maykumar-msft]

Description

1. Updating feature store classes name for private preview
2. Adding check for feature store property for private preview enabled in ml_client
3. updating imports in entities

If an SDK is being regenerated based on a new swagger spec, a link to the pull request containing these swagger spec changes has been included above.

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-ai-ml