Disable tel number detection on IOS

Any string pattern identifiable as a telephone
number is turned into a link on IOS devices by
default.

We use telephone numbers in several ways, in
particular to link to sms notifications, so need
this behaviour turned off unless specifically
required.

app/templates/admin_template.html

@@ -18,6 +18,9 @@
       .govuk-header__container { border-color: {{header_colour}} }
   </style>
   <meta name="google-site-verification" content="niWnSqImOWz6mVQTYqNb5tFK8HaKSB4b3ED4Z9gtUQ0" />
+  {% block meta_format_detection %}
+    <meta name="format-detection" content="telephone=no">
+  {% endblock %}
   {% block meta %}
   {% endblock %}
 {% endblock %}