Link to new dashboard Addons page in old dashboard settings. (#11678)

* Link to new dashboard Addons page in old dashboard settings.

This is just using the same pattern as for versions,
but linking to another dashboard.
Could use an external icon here,
but didn't want to get too deep :)

* Fix up link

* Fix up docstring

readthedocs/templates/projects/project_edit_base.html

@@ -15,6 +15,8 @@
     <div class="navigable">
       <ul>
         <li class="{% block project-edit-active %}{% endblock %}"><a href="{% url "projects_edit" project.slug %}">{% trans "Settings" %} </a></li>
+        <!-- Link the Addons on the new dashboard. Can't reverse the URL. -->
+        <li><a href="//app.{{ PRODUCTION_DOMAIN }}/dashboard/{{ project.slug }}/addons/edit/">{% trans " Addons" %}</a></li>
         <!-- Add a link to the dashboard versions page so users can find it -->
         <li><a href="{% url "project_version_list" project.slug %}">{% trans "Edit Versions" %}</a></li>
         <li class="{% block project-domains-active %}{% endblock %}"><a href="{% url "projects_domains" project.slug %}">{% trans "Domains" %}</a></li>