Add question about research consent

Since GDPR came into effect it’s less clear about whether we can
contact teams for user research purposes.

If we make people opt-in (or not) we know we’re safe to contact them (or
not).

Since we mostly care about how services are using Notify for real (ie
live services) or services that are considering adopting it (ie those
who have contacted us with a question) it feels like the go-live process
is the most appropriate place to collect this consent.

app/main/forms.py

@@ -581,6 +581,14 @@ class RequestToGoLiveForm(StripWhitespaceForm):
         'How many letters do you expect to send in the next year?',
         validators=[DataRequired(message='Can’t be empty')]
     )
+    research_consent = RadioField(
+        'Can we contact you when we’re doing user research?',
+        choices=[
+            ('yes', 'Yes'),
+            ('no', 'No'),
+        ],
+        validators=[DataRequired()]
+    )
 
 
 class ProviderForm(StripWhitespaceForm):