Rename selection to options as per the changes

Closes #176 (closed)

Per the release notes of mkdocstrings 0.19.0, selection key has to be renamed to options

docs/ref/api/classification.md

 # Classification
 
 ::: arkindex_worker.worker.classification
-    selection:
+    options:
       members: no
 
 ::: arkindex_worker.worker.classification.ClassificationMixin