🚸 [#4320] Update stories and UX of completion view

The backend will gain the ability to include the cosign link/button,
which will be rendered as a primary button. To point out the
right call to actions, the 'return to website' link has been
made a secondary button/action.

Stories have been updated to reflect the default templates in the
backend.

src/components/PostCompletionViews/ConfirmationViewCosign.stories.js

@@ -16,6 +16,17 @@ export default {
     confirmationPageContent: `
       <p>Your request is not yet complete.</p>
       <h2>Cosigning required</h2>
+      <p>
+        You can start the cosigning immediately by clicking the button below.
+      </p>
+      <p>
+        <a href="./start-cosign">
+          <button type="button" class="utrecht-button utrecht-button--primary-action">
+            Cosign now
+          </button>
+        </a>
+      </p>
+      <h3>Alternative instructions</h3>
       <p>
         We've sent an email with a cosign request to
         <a href="mailto:[email protected]">[email protected]</a>. Once the submission has

src/components/PostCompletionViews/PostCompletionView.jsx

@@ -42,7 +42,7 @@ const PostCompletionView = ({
         <Toolbar>
           <ToolbarList>
             <Anchor href={mainWebsiteUrl} rel="noopener noreferrer">
-              <OFButton appearance="primary-action-button">
+              <OFButton appearance="secondary-action-button">
                 <FormattedMessage
                   description="Back to main website link title"
                   defaultMessage="Return to main website"