Domain Split Updates to Data API

[taija]

New students will be created in a different domain starting likely before Fall 2025. Updates will need to be made in order to ensure correct usernames are exposed on student endpoints

• Update /app/Http/Transformers/StudentTransformer to remove usage of NTUserName column, which only will work for pre-split student accounts.
• Add GUID value to /app/Http/Transformers/StudentTransformer to allow for better integration with SSO as needed.
• Add GUID value to /app/Http/Transformers/EmployeeTransformer to allow for better integration with SSO as needed.