feat: add enrollment timestamp to at-risk learners (FC-0051)

[SoryRawyer]

This change adds the timestamp of when a learner enrolled in a course to the fact_student_status model. This field is then used in dim_at_risk_learners to support displaying a distribution of when at-risk learners enrolled in the course.

[openedx-webhooks]

Thanks for the pull request, @SoryRawyer! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

All technical communication about the code itself will be done via the GitHub pull request interface. As a reminder, our process documentation is here.

Please let us know once your PR is ready for our review and all tests are green.

[bmtcril]

This is the most recent enrollment time, right? So when a user changes status (upgrades to certificate or unenrolls and re-enrolls) the clock resets? We should probably include that detail in the model docs for this and fact_enrollment_status.

[SoryRawyer]

That's a good point. Yes, it should be the most recent enrollment action timestamp.

[openedx-webhooks]

@SoryRawyer 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.

[bmtcril]

Released as v3.22.0, tutor plugin PR is here: openedx/tutor-contrib-aspects#763