Create task for sending out email notifications for soon-to-expire ECA documents

As part of the MVP of this project, the API should support sending out email notifications to users when the active ECA document is soon to expire. This should have multiple intervals, and should track when users have been sent notifications as to not oversend messages. Initially, we will have 2 intervals for this notification at 1 week before expiration, and 1 month before expiration.