Repoint footer and homepage links

Performance Platform is going away at 10am on Monday, so let’s point to
our Performance Page instead.

app/templates/admin_template.html

@@ -172,7 +172,7 @@
             "text": "System status"
           },
           {
-            "href": "https://www.gov.uk/performance/govuk-notify",
+            "href": url_for('main.performance'),
             "text": "Performance data"
           },
           {

app/templates/views/signedout.html

@@ -135,7 +135,7 @@
       </div>
       <p class="govuk-body">
         See the
-        <a class="govuk-link govuk-link--no-visited-state" href="https://www.gov.uk/performance/govuk-notify/government-services">list of services and organisations</a>.
+        <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('main.performance') }}">list of services and organisations</a>.
       </p>
     </div>
   </div>

tests/app/main/views/test_index.py

@@ -40,8 +40,8 @@ def test_non_logged_in_user_can_see_homepage(
         '9,999 services '
         'See the list of services and organisations.'
     )
-    assert page.select_one('#whos-using-notify a')['href'] == (
-        'https://www.gov.uk/performance/govuk-notify/government-services'
+    assert page.select_one('#whos-using-notify a')['href'] == url_for(
+        'main.performance'
     )