Make MOU a multiple choice question not a banner

If we want someone to read something (ie that they need to have the MOU
signed), then the best way is to make them interact with it.

And if someone doesn’t have the MOU in place, then we need to know to
send them a copy. The best way of them telling us this is in this form,
rather than sending them to the generic contact form and have them
compose a message saying ‘please send me the MOU thanks’, which we
haven’t seen anyone actually do.

app/main/forms.py

@@ -350,6 +350,18 @@ class Feedback(Form):
 
 
 class RequestToGoLiveForm(Form):
+    mou = RadioField(
+        (
+            'Has your organisation accepted the GOV.UK Notify data sharing and financial '
+            'agreement (Memorandum of Understanding)?'
+        ),
+        choices=[
+            ('yes', 'Yes'),
+            ('no', 'No – we’ll send you a copy'),
+            ('don’t know', 'I don’t know – we’ll check for you')
+        ],
+        validators=[DataRequired()]
+    )
     channel = RadioField(
         'What kind of messages will you be sending?',
         choices=[