Add what we know of agreements to go live request

When we process a go live request it’s a pain to have to go fishing in
the Google Drive to see if there’s a signed agreement in there. This
should make it easier when we know there’s already an agreement.

tests/app/main/views/test_service_settings.py

@@ -530,6 +530,7 @@ def test_should_redirect_after_request_to_go_live(
     returned_message = mock_post.call_args[1]['message']
     assert 'On behalf of service one' in returned_message
     assert 'Organisation type: central' in returned_message
+    assert 'Agreement signed: None (None)' in returned_message
     assert 'Channel: email and text messages' in returned_message
     assert 'Start date: 01/01/2017' in returned_message
     assert 'Start volume: 100,000' in returned_message