Omit default values for attributes.

We copy the mkdocstrings template for attributes so that we can exclude the (default) value for attributes (and class variables) from the documentation as that is generally useless.

mkdocs.yml

@@ -251,6 +251,7 @@ plugins:
 - search:
 - autorefs:
 - mkdocstrings:
+    custom_templates: docs/_templates
     default_handler: python
     handlers:
         python: