LTI Advantage in its various specifications support for exchanging and syncing due date. This ticket is to add support for the part of the specifications that relate to due date interoperability:

1. Moodle supports the ResourceLink.submission.endDateTime substitution parameter to communicate the due date if the tool configured itself to receive as custom parameter
   1. Dates are communicated using ISO 8601 format
   2. If there is no due date, blank is used as the value
2. Moodle supports setting the due date when importing an item through deep linking
   1. if present in the link definition in deep linking use submission.endDateTime to set the completion date
3. When a line item is updated with endDateTime value, and the line item is linked to an activity, update that activity completion date accordingly.

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Edited to change 'activity completion date' to 'due date', as explained in the comments.