fix: improve migration of existing tags

program/migrations/0073_alter_note_tags.py

 # Generated by Django 4.2.2 on 2023-09-06 02:31
+import json
 
 from django.db import migrations, models
 
 
+def split_old_tags(apps, _):
+    Note = apps.get_model("program", "Note")
+
+    for note in Note.objects.exclude(old_tags=""):
+        note.tags = json.dumps([tag.strip() for tag in note.old_tags.split(",")])
+
+        note.save()
+
+
 class Migration(migrations.Migration):
     dependencies = [
         ("program", "0072_timeslot_language_timeslot_topic"),
     ]
 
     operations = [
-        migrations.AlterField(
+        migrations.RenameField(
             model_name="note",
-            name="tags",
+            new_name="old_tags",
+            old_name="tags",
+        ),
+        migrations.AddField(
             field=models.JSONField(blank=True),
+            model_name="note",
+            name="tags",
         ),
+        migrations.RunPython(code=split_old_tags),
+        migrations.RemoveField(
+            model_name="note",
+            name="old_tags",
+        )
     ]