Feature/add warehouse models for cohorts

[sleblanc23]

Description & motivation

Adds warehouse models for cohorts, per the EDU Project Development board.

Requires a field added to stg_ef3__cohorts in this PR.

PR Merge Priority:

• Low

New files created:

• dim_cohort.sql
• fct_student_cohort_association.sql

Tests and QC done:

• Ran the models successfully in GSN and South Carolina

Future ToDos:

No implementations have data for staffCohortAssociations yet. I added a Monday task to build fct_staff_cohort_association once we have a use case.

[ejoranlienea]

Looks good.
Two thoughts:

1. Could consider adding an active indicator, like student_school_association has
2. Given how rarely (if ever) we've seen this data in the wild, I wonder if we should tag this under its own domain here and in source so that we can disable it when not in use.

[sleblanc23]

@ejoranlienea

I added an active indicator and a cohort tag so we can disable these when they're not needed. Also opened a PR in source for those models. Am I missing anything for adding that tag?