Notifications: show attached to User, Project and Organization

Render notifications attached to these objects.
This is the first pass of this work and there are some things we need to make
decisions and improve.

- Where (what pages) these notifications should render?
- How "global" they should be considered?

Note we are rendering these notifications in the template for now,
but in the future they will be rendered using the APIv3: #259

readthedocsext/theme/templates/includes/utils/messages.html

@@ -7,6 +7,23 @@
   page content pane.
 {% endcomment %}
 
+{% comment %}
+``user_notifications`` comes from a Context Processor.
+We need to use a CustomUser to have access to "user.notifications"
+See https://docs.djangoproject.com/en/4.2/ref/settings/#std-setting-AUTH_USER_MODEL
+{% endcomment %}
+{% if user_notifications %}
+  {% for notification in user_notifications %}
+    <div class="ui message">
+    {% comment %}
+    Add this Xmark here once we implement dismissing notifications.
+    <i class="fa-duotone fa-circle-xmark close icon"></i>
+    {% endcomment %}
+      {{ notification.get_message.get_rendered_body|safe }}
+    </div>
+  {% endfor %}
+{% endif %}
+
 {% if messages %}
   {% for message in messages %}
     {% comment %}

readthedocsext/theme/templates/organizations/partials/header.html

@@ -126,4 +126,13 @@
     </div>
   {% endblock organization_header_navigation %}
 
+{# Render all the notifications attached to the organization.#}
+  {% for notification in organization.notifications.all %}
+    <div class="ui message">
+      <i class="fa-solid {{ notification.get_message.get_display_icon_classes }}"></i>
+      <span>{{ notification.get_message.get_rendered_body|safe }}</span>
+    </div>
+  {% endfor %}
+
+
 {% endblock organization_header %}

readthedocsext/theme/templates/projects/partials/header.html

@@ -201,4 +201,12 @@
     </div>
   {% endblock project_header_navigation %}
 
+{# Render all the notifications attached to the project.#}
+  {% for notification in project.notifications.all %}
+    <div class="ui message">
+      <i class="fa-solid {{ notification.get_message.get_display_icon_classes }}"></i>
+      <span>{{ notification.get_message.get_rendered_body|safe }}</span>
+    </div>
+  {% endfor %}
+
 {% endblock project_header %}