Adding views to view, add and edit service data retention policies.

Only visible to a platform admin.
A service can have a custom number of days to retain the notification data for each notification type.

app/templates/views/service-settings/data-retention.html

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+{% extends "withnav_template.html" %}
+{% from "components/api-key.html" import api_key %}
+{% from "components/page-footer.html" import page_footer %}
+{% from "components/table.html" import row_group, row, text_field, edit_field, field, boolean_field, list_table with context %}
+
+{% block service_page_title %}
+  Email reply to addresses
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <div class="grid-row bottom-gutter">
+    <div class="column-two-thirds">
+      <h1 class="heading-large">
+        Data retention
+      </h1>
+    </div>
+   <div class="column-one-third">
+	    <a href="{{ url_for('.add_data_retention', service_id=current_service.id) }}" class="button align-with-heading">Add data retention</a>
+  </div>
+  </div>
+  <div class="grid-row bottom-gutter">
+      <div class="column-full">
+          By default data is kept for 7 days
+      </div>
+  </div>
+  <div class="user-list">
+    {% if not data_retention_settings %}
+      <div class="user-list-item">
+        <span class="hint">You haven’t added any data retention</span>
+      </div>
+    {% endif %}
+    {% for item in data_retention_settings %}
+      <div class="user-list-item">
+
+          <p>
+            {{ item.notification_type | format_notification_type }} notifications will be kept for {{ item.days_of_retention }} days
+              <a class="user-list-edit-link" href="{{ url_for('.edit_data_retention', service_id =current_service.id, data_retention_id = item.id) }}">Change</a>
+          </p>
+      </div>
+    {% endfor %}
+  </div>
+
+{% endblock %}