ui: Use HTMX to update notifications on partial page updates

Tests:

- When app install button is clicked, the new page shows that app is being
installed. However, when app installation is complete, the notification still
shows that app is being installed. With the patch, the issues is resolved.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/templates/notifications.html

@@ -8,7 +8,7 @@
 {% load static %}
 
 {% if notifications %}
-  <div class="notifications collapse no-no-js">
+  <div id="notifications" class="notifications collapse no-no-js" hx-swap-oob="true">
     <ul>
       {% for note in notifications %}
         <li class="notification notification-{{ note.severity }}">