UX: Apply new admin UI guidelines to What's New (#28454)

app/assets/javascripts/admin/addon/templates/whats-new.hbs

@@ -1,5 +1,16 @@
 <div class="admin-config-area">
-  <h2>{{i18n "admin.dashboard.new_features.title"}}</h2>
-  <p>{{html-safe (i18n "admin.dashboard.new_features.subtitle")}}</p>
+  <AdminPageHeader
+    @titleLabel="admin.dashboard.new_features.title"
+    @descriptionLabel="admin.dashboard.new_features.subtitle"
+    @learnMoreUrl="https://meta.discourse.org/tags/c/announcements/67/release-notes"
+  >
+    <:breadcrumbs>
+      <DBreadcrumbsItem
+        @path="/admin/whats-new"
+        @label={{i18n "admin.dashboard.new_features.title"}}
+      />
+    </:breadcrumbs>
+  </AdminPageHeader>
+
   <DashboardNewFeatures />
 </div>

config/locales/client.en.yml

@@ -5071,7 +5071,7 @@ en:
         problems_found: "Some advice based on your current site settings"
         new_features:
           title: "What's new"
-          subtitle: "For even more detail about new features and improvements we are adding all the time, see <a href='https://meta.discourse.org/tags/c/announcements/67/release-notes' target='_blank'>Release notes</a>."
+          subtitle: "We are releasing new features and improvements all the time. This page covers the highlights, but you can click 'Learn more' to see extensive release notes."
           previous_announcements: "You can see previous new feature announcements on <a href='%{url}' target='_blank'>Discourse Meta</a>"
           learn_more: "Learn more..."
         last_checked: "Last checked"