fixup! fixup! feat: Add slots to add tab links and add slots for plugin routes

Author: xitij2000

src/index.jsx

@@ -35,6 +35,7 @@ import CourseAccessErrorPage from './generic/CourseAccessErrorPage';
 import DecodePageRoute from './decode-page-route';
 import { DECODE_ROUTES, ROUTES } from './constants';
 import PreferencesUnsubscribe from './preferences-unsubscribe';
+import PageNotFound from './generic/PageNotFound';
 
 subscribe(APP_READY, () => {
   const root = createRoot(document.getElementById('root'));
@@ -50,6 +51,7 @@ subscribe(APP_READY, () => {
             <UserMessagesProvider>
               <div className="app-container">
                 <Routes>
+                  <Route path="*" element={<PageWrap><PageNotFound /></PageWrap>} />
                   <Route path={ROUTES.UNSUBSCRIBE} element={<PageWrap><GoalUnsubscribe /></PageWrap>} />
                   <Route path={ROUTES.REDIRECT} element={<PageWrap><CoursewareRedirectLandingPage /></PageWrap>} />
                   <Route