Not storing groups for documentations is kind of a problem

Today, I stumbled over a new edge case:

1. There was a lesson event without a course, but with a group (groups field) which has been documented in the coursebook (leads to documentation without any course or group information).
2. There is a student who has been marked as absent in this documentation.
3. Now, in the statistics overview of the group, the absent participation status of the student isn't counted because the documentation has no course.
4. In the personal overview of the student, the absence is counted.

Conclusion: It's a problem to only store the course with the documentation.

added part::backend type::bug workflow::current-todo workflow::discussing labels

Dev meeting decided: We store groups with the documentation as source of truth. Needs a migration to set groups for existings documentations (set from course, if course isn't set from amended lesson event).

removed workflow::discussing label

assigned to @permcu

changed milestone to /AlekSIS%"[NLnet #6 (closed)] Do integration/final tests with pilot schools"

added source::customer::kath label

assigned to @hansegucker and unassigned @permcu

created branch 351-not-storing-groups-for-documentations-is-kind-of-a-problem to address this issue

mentioned in merge request !476 (merged)

closed with merge request !476 (merged)

mentioned in commit 9e24f1ee