feat(widget-object): add collapsed option to collapse object by default (#3606)

dev-test/config.yml

@@ -124,6 +124,7 @@ collections: # A list of collections the CMS should be able to edit
       - label: 'Object'
         name: 'object'
         widget: 'object'
+        collapsed: true
         fields:
           - label: 'Related Post'
             name: 'post'

packages/netlify-cms-widget-object/src/ObjectControl.js

@@ -42,7 +42,7 @@ export default class ObjectControl extends React.Component {
   constructor(props) {
     super(props);
     this.state = {
-      collapsed: false,
+      collapsed: props.field.get('collapsed', false),
     };
   }
 

website/content/docs/widgets/object.md

@@ -10,6 +10,7 @@ The object widget allows you to group multiple widgets together, nested under a
 - **Data type:** list of child widget values
 - **Options:**
   - `default`: you can set defaults within each sub-field's configuration
+  - `collapsed`: if added and labeled `true`, the widget's content is collapsed by default
   - `fields`: (**required**) a nested list of widget fields to include in your widget
 - **Example:**
     ```yaml
@@ -27,6 +28,7 @@ The object widget allows you to group multiple widgets together, nested under a
         - label: "Address"
           name: "address"
           widget: "object"
+          collapsed: true
           fields: 
             - {label: "Street Address", name: "street", widget: "string"}
             - {label: "City", name: "city", widget: "string"}