Implement the EULA acceptance gate and webhook-based completion flow for Turnitin Core API (Similarity/TCA) submissions

Steps

1. After configuring the Turnitin URL and API key, call the Get Features Enabled request and check the returned tenant.require_eula flag to know whether your integration must show users a EULA before submitting.
2. If require_eula is true, call Get EULA Version Info with version_id=latest to get the current EULA version, then Get EULA Page to retrieve the EULA HTML (or use its static url) for display.
3. Before creating a submission, confirm the user has accepted the current EULA version; if not, show it and block submission until accepted, then pass the optional eula attributes on the Create Submission request.
4. Poll Get EULA Version Info roughly every 24 hours to detect a newly published EULA version, and re-prompt any user who hasn't accepted the new version.
5. Register for and consume webhooks for submission-complete and similarity-report-complete events instead of tight polling; fall back to polling the corresponding status endpoint only if no webhook arrives within about 30 minutes.