CCM-11492 Add invalid message plan page

Author: nicki-nhs

frontend/src/middleware.ts

@@ -21,8 +21,9 @@ const protectedPaths = [
   /^\/message-plans\/campaign-id-required$/,
   /^\/message-plans\/choose-message-order$/,
   /^\/message-plans\/create-message-plan$/,
-  /^\/message-templates$/,
+  /^\/message-plans\/invalid$/,
   /^\/message-plans$/,
+  /^\/message-templates$/,
   /^\/nhs-app-template-submitted\/[^/]+$/,
   /^\/preview-email-template\/[^/]+$/,
   /^\/preview-letter-template\/[^/]+$/,