Convert HTML metadatas as markdown

Closes #78 (closed)

arkindex/documents/serializers/light.py

 import markdown
 from django.db.models import Max
-from html_sanitizer import Sanitizer
+from html_sanitizer.django import get_sanitizer
 from rest_framework import serializers
 from rest_framework.exceptions import APIException, ValidationError
 
@@ -106,7 +106,7 @@ class MetaDataLightSerializer(serializers.ModelSerializer):
     def to_representation(self, instance):
         # The value must be HTML
         if instance.type == MetaType.Markdown:
-            sanitizer = Sanitizer()
+            sanitizer = get_sanitizer()
             html = markdown.markdown(instance.value)
             instance.value = sanitizer.sanitize(html)
         return super().to_representation(instance)