Project Import Status is not exposed via the API

Summary

If a project is forked via the API, this will schedule a job to create the repo import the forked repo's data. The call will return immediately. Currently, there is no way to determine whether the deferred fork operation has successfully completed in the background, as the import_status for the project is not exposed via the API.

Proposed Changes

Expose the import_status field on the Project entity, to allow our API users to determine when the fork operation has completed successfully.

Additional Details

Relevant Zendesk ticket: https://gitlab.zendesk.com/agent/tickets/29433