Add {% block pluginfooter %} to 'base/layout.html' template

Makes it easy to insert footer information into Netbox footer.

netbox/templates/base/layout.html

@@ -108,6 +108,9 @@
 
         {# Page footer #}
         <footer class="footer container-fluid">
+          {# Plugin Custom Footer #}
+          {% block pluginfooter %}{% endblock %}
+
           <div class="row align-items-center justify-content-between mx-0">
 
             {# Docs & Community Links #}