Add basic view to the settings page

This commit adds:
- a row to the settings page…
- …which links to a page explaining what basic view is

The new row (and link) will only appear for services who already have
the feature switched on. This is because we are not launching the
feature yet, so it shouldn’t be available to just anyone.

tests/app/main/views/test_service_settings.py

@@ -170,6 +170,22 @@ def test_should_show_overview(
         'Send letters Off Change',
 
     ]),
+    (['letters', 'caseworking'], [
+
+        'Service name service one Change',
+        'Sign-in method Text message code Change',
+        'Basic view On Change',
+
+        'Label Value Action',
+        'Send emails Off Change',
+
+        'Label Value Action',
+        'Send text messages Off Change',
+
+        'Label Value Action',
+        'Send letters Off Change',
+
+    ]),
 ])
 def test_should_show_overview_for_service_with_more_things_set(
         client,
@@ -2374,6 +2390,16 @@ def test_invitation_pages(
     assert normalize_spaces(page.select('main p')[0].text) == expected_p
 
 
+def test_see_basic_view_page(
+    client_request,
+):
+    page = client_request.get(
+        "main.service_set_basic_view",
+        service_id=SERVICE_ONE_ID
+    )
+    assert page.h1.text.strip() == 'Basic view'
+
+
 def test_service_settings_when_inbound_number_is_not_set(
     logged_in_client,
     service_one,