Add ListCorpusWorkerVersions endpoint

Closes #537 (closed)

arkindex/dataimport/serializers/workers.py

@@ -34,6 +34,7 @@ class WorkerVersionSerializer(serializers.ModelSerializer):
     # ModelSerializer does not yet support Django 3.1's JSONField
     # https://github.com/encode/django-rest-framework/pull/7467
     configuration = serializers.JSONField()
+    element_count = serializers.IntegerField(read_only=True)
 
     class Meta:
         model = WorkerVersion
@@ -46,6 +47,7 @@ class WorkerVersionSerializer(serializers.ModelSerializer):
             'docker_image_name',
             'state',
             'worker',
+            'element_count',
         )
         read_only_fields = ('docker_image_name',)
         # Avoid loading all revisions and all Ponos artifacts when opening this endpoint in a browser