Edx-proctoring

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* If an attempt transitions from `ready_to_submit` back to `started`, the proctoring provider
backend function `start_exam_attempt` will not be called.

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* If the Django setting `PROCTORED_EXAM_VIEWABLE_PAST_DUE` is false, exam content will not be viewable past
an exam's due date, even if a learner has acknowledged their status.
* Extend exam attempt API to return exam type and to check if
user has satisfied prerequisites before taking proctored exam.
* Extend proctoring settings API to return additional data about proctoring
provider.
* Add API endpoint which provides exam review policy for specific exam.
Usage case is to provide required data for the learning app MFE.

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* If the `is_integrity_signature_enabled` waffle flag is turned on, do not render the ID verification
template for proctored exams.

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* Add logging for attempt status transitions caused by a time out or reattempt

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* Fix a bug where we are to pass to vendor javascript a value in milliseconds, instead of just seconds

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* Use the same DEFAULT_DESKTOP_APPLICATION_PING_INTERVAL_SECONDS interval to start the exam and ping the
proctoring desktop applicaiton