Update example and documentation for JS file upload

Author: DavidBiddle

guide/content/form-elements/file-upload.slim

@@ -14,4 +14,8 @@ p.govuk-body
   caption: 'File upload with label and hint',
   code: file_upload)
 
+== render('/partials/example.*',
+  caption: 'Javascript-enhanced file upload with label and hint',
+  code: file_upload_javascript)
+
 == render('/partials/related-navigation.*', links: file_info)

guide/lib/examples/file.rb

@@ -7,5 +7,14 @@ def file_upload
           hint: { text: 'Upload a clear colour photograph of yourself looking straight at the camera' }
       SNIPPET
     end
+
+    def file_upload_javascript
+      <<~SNIPPET
+        = f.govuk_file_field :profile_photo,
+          label: { text: 'Identification photograph' },
+          hint: { text: 'Upload a clear colour photograph of yourself looking straight at the camera' },
+          javascript: true
+      SNIPPET
+    end
   end
 end

lib/govuk_design_system_formbuilder/builder.rb

@@ -1046,6 +1046,7 @@ def govuk_fieldset(legend: { text: 'Fieldset heading' }, caption: {}, described_
     # @option kwargs [Hash] kwargs additional arguments are applied as attributes to the +input+ element
     # @param form_group [Hash] configures the form group
     # @option form_group kwargs [Hash] additional attributes added to the form group
+    # @param javascript [Boolean] Configures whether to add HTML for the javascript-enhanced version of the component
     # @param block [Block] arbitrary HTML that will be rendered between the hint and the input
     #
     # @example A photo upload field with file type specifier and injected content