Remove email features page from search engines

Reimplements https://github.com/alphagov/notifications-aws/pull/796

Since deploying alphagov/notifications-utils#736 I’ve been looking at
how members of the public are ending up on our support page. The vast
majority are landing on https://www.notifications.service.gov.uk/features/email

Previously we thought that they were clicking the ‘contact us’ link in
the page, which deep linked into the support journey, so we removed
these deep links in alphagov/notifications-admin#3451

But the tickets are still coming in, so I think that people are still
landing on this page, then going directly to ‘support’ in the top
navigation. So the next measure we have available is to try to stop
people from landing on this page in the first place. All the examples
I’ve looked at show people coming from Google to this page. By putting
the page’s URL in our robots.txt it should stop Google (and other search
engines) listing it in search results.

app/main/views/index.py

@@ -21,7 +21,7 @@ from app.main.views.sub_navigation_dictionaries import (
     using_notify_nav,
 )
 from app.models.feedback import QUESTION_TICKET_TYPE
-from app.utils import get_logo_cdn_domain
+from app.utils import get_logo_cdn_domain, hide_from_search_engines
 
 
 @main.route('/')
@@ -253,6 +253,7 @@ def roadmap():
 
 
 @main.route('/features/email')
+@hide_from_search_engines
 def features_email():
     return render_template(
         'views/features/emails.html',

tests/app/main/views/test_index.py

@@ -88,6 +88,7 @@ def test_robots(client):
     ('bat_phone', {}),
     ('thanks', {}),
     ('register', {}),
+    ('features_email', {}),
     pytest.param('index', {}, marks=pytest.mark.xfail(raises=AssertionError)),
 ))
 @freeze_time('2012-12-12 12:12')  # So we don’t go out of business hours