Capture concept of "Responsible Teacher"

The original issue, somewhat lightly edited. Came up in Indiana DOE

... scenarios where the students in the same section will have different staff that are responsible for the student's progress. In many cases these are counselors rather than someone in the actual classroom. In these cases, we need a way to associate a specific student, section, and staff member together.

In the SIS, students can have a 'responsible teacher' assigned at the student level or at the section enrollment level. This allows schools to specify who is responsible for a student's progress when it's different from the actual teacher in the room.

• One approach would be to publish staffSectionAssociations for all the staff who have responsibility for students in the section. However, that still doesn't provide a way to specify which staff is responsible for which student.
• I've also considered creating section-based cohorts or staff-based cohorts, but in either case we would need a cohort for every combination of responsible staff and section.
• Another approach is publishing 'dummy' sections for each combination of section and responsible staff, using the teacher SPN as a suffix on the section identifier and publishing studentSectionAssociations in the appropriate 'dummy' section. The major drawback is this is inventing data on the fly, and also that this hinges on the immutability of section identifiers throughout other Ed-Fi resources.
• Yet another approach is requiring schools to create separate sections for each combination of student, section, and responsible staff. This adds substantial workload and imposes an artificial structure on the real-world classroom that makes tracking attendance, assignments, and grades more difficult.
• A simpler approach would be to add ResponsibleStaff as an IN DOE extension element on studentSectionAssociations. If blank, then the section teacher of record is the responsible staff, so nothing currently existing would be broken.

Adding this last field would be a relatively minor change that could be readily implemented and would solve an otherwise messy problem, without causing new work for the districts or publishing dummy sections that could cause integrity problems with other resources. Even better, it would reflect the real-world classroom situation in the data.