Fix bug with collapsed metadata fieldset being hidden in JSON dump plugin

src/openforms/js/components/admin/form_design/registrations/json_dump/JSONDumpOptionsForm.js

@@ -65,6 +65,7 @@ const JSONDumpOptionsForm = ({name, label, schema, formData, onChange}) => {
               defaultMessage="Metadata variables"
             />
           }
+          extraClassName="openforms-fieldset"
           collapsible
           initialCollapsed
         >

src/openforms/scss/components/admin/_fieldset.scss

@@ -0,0 +1,8 @@
+/**
+ * The django admin `.collapsed` styling on fieldset elements sets `overflow: hidden;`.
+ * Seeing how we already hide the fieldset content in the javascript code,
+ * the `overflow: hidden;` only hides the fieldset toggle (which we want to keep visible)
+ */
+.openforms-fieldset.collapsed {
+  overflow: visible !important;
+}

src/openforms/scss/components/admin/_index.scss

@@ -19,6 +19,7 @@
 @import './column-field-value';
 @import './confirmation-email-template';
 @import './variablemapping';
+@import './fieldset';
 
 // Form design UI
 @import './select';