Show email reply to address if one’s been selected

If you’ve picked an email reply to address, it’s good UI design to have
your choice played back to you, so you can be confident it’s worked.
This commit does that by making it part of the email preview.

Uses:
- [ ] https://github.com/alphagov/notifications-utils/pull/227

app/main/views/send.py

@@ -323,7 +323,8 @@ def send_test_step(service_id, template_id, step_index):
             template_id=template_id,
             filetype='png',
         ),
-        page_count=session['send_test_letter_page_count']
+        page_count=session['send_test_letter_page_count'],
+        email_reply_to=get_email_reply_to_address_from_session(service_id),
     )
 
     placeholders = fields_to_fill_in(
@@ -448,7 +449,6 @@ def _check_messages(service_id, template_type, upload_id, letters_as_pdf=False):
     remaining_messages = (current_service['message_limit'] - sum(stat['requested'] for stat in statistics.values()))
 
     contents = s3download(service_id, upload_id)
-
     template = get_template(
         service_api_client.get_service_template(
             service_id,
@@ -462,7 +462,8 @@ def _check_messages(service_id, template_type, upload_id, letters_as_pdf=False):
             template_type=template_type,
             upload_id=upload_id,
             filetype='png',
-        ) if not letters_as_pdf else None
+        ) if not letters_as_pdf else None,
+        email_reply_to=get_email_reply_to_address_from_session(service_id),
     )
     recipients = RecipientCSV(
         contents,
@@ -726,7 +727,8 @@ def _check_notification(service_id, template_id, exception=None):
     template = get_template(
         db_template,
         current_service,
-        show_recipient=True
+        show_recipient=True,
+        email_reply_to=get_email_reply_to_address_from_session(service_id),
     )
 
     # go back to start of process
@@ -805,3 +807,10 @@ def send_notification(service_id, template_id):
         notification_id=noti['id'],
         help=request.args.get('help')
     ))
+
+
+def get_email_reply_to_address_from_session(service_id):
+    if session.get('sender_id'):
+        return service_api_client.get_reply_to_email_address(
+            service_id, session['sender_id']
+        )['email_address']