Add Thumbnails generator into system workers

arkindex/system_workers.yml

@@ -36,3 +36,8 @@ features:
             name: arkindex/workers/generic-training-dataset
             version: 0.3.0
             slug: generic-training-dataset
+    thumbnails_generator:
+        teklia_worker:
+            name: arkindex/workers/thumbnails
+            version: 0.2.0
+            slug: thumbnails-generator