Refactor /data-export/export

Overview
It seems redundant to pass entire file definition to start an export job, just the FileDefinitionId should be enough to fetch the details on the backend.
It should also check if the FileDefinition status is completed(file is uploaded completely), and only then start the export process

Acceptance Criteria

• schema modified to remove all redundant details
• unit tests
  API tests updated Will be moved to a separate story