Add 'opmerking' column to assessments and implement related functionality

- Updated the database migration to include an 'opmerking' column in the assessments table.
- Modified the Assessment model to include the new 'opmerking' field.
- Enhanced the API to handle saving and retrieving remarks associated with assessments.
- Updated the frontend to display and edit remarks in the assessments table.

backend/migrations/versions/0002_assessment_opmerking.py

@@ -1,4 +1,4 @@
-"""assessment: voeg opmerking kolom toe
+"""assessment: voeg opmerking kolom toe 
 
 Revision ID: 0002
 Revises: 0001