Add service-specific versions of agreement page

Our usability testing found that jumping out of the service when going
to download the agreement made it difficult for people to find their way
back to the ‘Request to go live’ page.

This commit adds a duplicate, service-specific versions of these pages
which have the same content but:
- keep the service navigation
- have a link back to the ‘Request to go live’ page

tests/app/main/views/test_agreement.py

@@ -4,7 +4,7 @@ from io import BytesIO
 import pytest
 from flask import url_for
 
-from tests.conftest import mock_get_organisation_by_domain
+from tests.conftest import SERVICE_ONE_ID, mock_get_organisation_by_domain
 
 
 class _MockS3Object():
@@ -16,6 +16,22 @@ class _MockS3Object():
         return {'Body': BytesIO(self.data)}
 
 
+@pytest.mark.parametrize('endpoint, extra_args, link_selector, expected_back_links', [
+    (
+        'main.agreement',
+        {},
+        'main .column-two-thirds a',
+        []
+    ),
+    (
+        'main.service_agreement',
+        {'service_id': SERVICE_ONE_ID},
+        'main .column-five-sixths a',
+        [
+            partial(url_for, 'main.request_to_go_live', service_id=SERVICE_ONE_ID)
+        ]
+    ),
+])
 @pytest.mark.parametrize('agreement_signed, crown, expected_links', [
     (
         True, True,
@@ -44,17 +60,23 @@ def test_show_agreement_page(
     client_request,
     mocker,
     fake_uuid,
+    mock_has_jobs,
     agreement_signed,
     crown,
     expected_links,
+    endpoint,
+    extra_args,
+    link_selector,
+    expected_back_links,
 ):
     mock_get_organisation_by_domain(
         mocker,
         crown=crown,
         agreement_signed=agreement_signed,
     )
-    page = client_request.get('main.agreement')
-    links = page.select('main .column-two-thirds a')
+    expected_links = expected_back_links + expected_links
+    page = client_request.get(endpoint, **extra_args)
+    links = page.select(link_selector)
     assert len(links) == len(expected_links)
     for index, link in enumerate(links):
         assert link['href'] == expected_links[index]()