Create school level column without OD on base_powerschool__student_enrollments

[anthonygwalters]

For accountability metrics (ie. ADA & suspension rates), we need a version of school level that doesn't break out out-of-district placements as a separate school level from ES, MS, HS. This new column would just include those three options - ES, MS, and HS. For now, I'm crosswalking this, but it would be good to have it on the base view to avoid unnecessary joins in many data sources.

Thanks!