Added an administrator fallback banner to organisation join approval emails

templates/mail/organisation-membership-request.html.twig

@@ -3,6 +3,12 @@
 {% endblock %}
 
 {% block body %}
+{% if admin_fallback %}
+<hr style="color: #990000" />
+<h3 style="color: #990000">You are receiving this email as an organisation/site administrator!</h3>
+<p style="color: #990000">This email has been sent to you in lieu of <b>{{organisation.name}}</b> as there are currently no approved administrators for the organisation.</p>
+<hr style="color: #990000" />
+{% endif %}
 <p>
     Dear {{recipient.first_name}},
 </p>