employee_record: Fix the archive serialized as string once and for all

See 37c890f for rational, and
adccc5f for things we had to do since.

itou/employee_record/migrations/0002_fix_archived_json_as_string.py

@@ -0,0 +1,36 @@
+import json
+import time
+
+from django.db import migrations
+
+
+def forward(apps, schema_editor):
+    print()
+    EmployeeRecord = apps.get_model("employee_record", "EmployeeRecord")
+    total_updated = 0
+    to_update = []
+    for obj in EmployeeRecord.objects.filter(archived_json__isnull=False, archived_json__startswith='"{').only(
+        "pk", "archived_json"
+    ):
+        obj.archived_json = json.loads(obj.archived_json)
+        to_update.append(obj)
+        if len(to_update) % 1000 == 0:
+            total_updated += EmployeeRecord.objects.bulk_update(to_update, {"archived_json"})
+            print(f"{total_updated} objects updated")
+            to_update = []
+            time.sleep(0.5)
+    if to_update:
+        total_updated += EmployeeRecord.objects.bulk_update(to_update, {"archived_json"})
+        print(f"{total_updated} objects updated")
+
+
+class Migration(migrations.Migration):
+    atomic = False
+
+    dependencies = [
+        ("employee_record", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.RunPython(code=forward, reverse_code=migrations.RunPython.noop, elidable=True),
+    ]