[BB-4015] Cronjob for getting monthly active user count
Description
This adds a task similar to the existing monthly report. It sends an email with the number of logged in users for the past month for each instance.
Supporting information
BB-4015
Testing instructions
The management script can be run manually and it will generate a CSV.
The Huey task can be tested by setting it to run more frequently (on stage?) and check whether the results are ok.
Other information
It may make sense to refactor this, as the new periodic task is very similar of the existing one. The crontab setting may need to be different so it does not reuse the exact same ones as the other report task.