Stop live services requesting to go live

Live services shouldn't be able to request to go live again. Once a
service is live we remove the option to go live from the Settings page,
but we still link to the page to request to go live from other places
e.g. the 'Get started' page. As a result, we've seen some services make
another request to go live when their service has already been live for
months - this change will stop that from happening.

app/main/views/service_settings.py

@@ -187,6 +187,9 @@ def estimate_usage(service_id):
 @main.route("/services/<uuid:service_id>/service-settings/request-to-go-live", methods=['GET'])
 @user_has_permissions('manage_service')
 def request_to_go_live(service_id):
+    if current_service.live:
+        return render_template('views/service-settings/service-already-live.html')
+
     return render_template(
         'views/service-settings/request-to-go-live.html'
     )

app/templates/views/service-settings/service-already-live.html

@@ -0,0 +1,28 @@
+{% extends "withnav_template.html" %}
+{% from "components/page-header.html" import page_header %}
+
+{% block service_page_title %}
+  Your service is already live
+{% endblock %}
+
+{% block maincolumn_content %}
+  <div class="govuk-grid-row">
+    <div class="govuk-grid-column-full">
+      {{ page_header('Your service is already live') }}
+
+      <p class="govuk-body">
+        {% if current_service.go_live_at %}
+          ‘{{ current_service.name }}’ went live on {{ current_service.go_live_at | format_date_normal }}.
+        {% else %}
+          ‘{{ current_service.name }}’ is already live.
+        {% endif %}
+        </p>
+
+      <p class="govuk-body">
+        <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.choose_account') }}">Switch service</a>
+         if you want to make a different service live.
+      </p>
+
+    </div>
+  </div>
+{% endblock %}