Merge pull request #19241 from overleaf/jel-cms-btn-premium

[web] Render premium button style from CMS

GitOrigin-RevId: 5cd896e6f220f48054fa9fe35b48a56449facf6a

services/web/frontend/stylesheets/components/buttons.less

@@ -158,6 +158,9 @@
   .btn-secondary {
     .btn-secondary;
   }
+  .btn-premium {
+    .btn-premium;
+  }
 }
 
 // Link buttons