Report billable active students and teachers by login

**Report on who and when users "sign into" the LMS app.**

We bill by user. Today we define billable as signing in. This way we can charge for:

- Teachers who never annotate
- Students who never annotate, either because
- their teacher has created reading assignments and added footnotes, but not required students to actually annotate, or
- because they _should_ be using the app but aren't motivated enough to actually do the assignment.
- And **not** charge for students who enrolled in a class but then dropped out.

We need to be able to answer in near real-time questions like:

- how many users have signed in this period?
- year? academic year?
- semester? academic semester?
- month?
- week?
- day?
- how many users have signed in at all? (these should lead ARR)
- over time?
- how many users are billable for a given institution?
- Where are those billable users coming from? In other words, which teachers, courses, disciplines, and sub-accounts (campuses, schools, and colleges)?
- how many users of a given role have signed in in a given period?
- teachers?
- students?
- admins (buyers or points of contact)

In the LMS context, we are currently happy using the app launch as sign-in.

Places where this data shows up:

- Board report: needs a billable active users chart
- Product performance report: needs a billable active users chart
- Hubspot report: Replace existing active counts with sign-in
- Sales and success need the active user's number by semester updated in HubSpot
- Groups query: Sales and success need the active users number pulled into a spreadsheet they can share with customers
- Dashboard replacement: customers need to be able to see their billable active users

## Constraints

- This needs to work only for sign-ins post-implementation.

## Notes

- This story isn't about all active users, but we're focusing more about getting more teacher leads from freemium and expect that to be a future story
- I left off time granularity as I don't expect to need it this time around, but you could expect us to use this in the future as we look at when during the day users are signing in. This is useful to understand for both student and teacher user experiences, e.g., if we see students often work late at night, we could time a "helpful tips" campaign for the same time.
- This story isn't about the free app, but you can expect a similar desire in the future around free app users, especially because we may want to eventually deliver an education app **separate** from the LMS LTI integration.

## Related

Related to https://github.com/hypothesis/private-issues/issues/135

Related to https://github.com/hypothesis/private-issues/issues/128