Check service is not in trial mode for uploaded letters

This adds an api check that the service is not in trial mode when
someone tries to send an uploaded letter.

app/service/send_notification.py

@@ -140,6 +140,13 @@ def send_pdf_letter_notification(service_id, post_data):
     check_service_has_permission(UPLOAD_LETTERS, service.permissions)
     check_service_over_daily_message_limit(KEY_TYPE_NORMAL, service)
     validate_created_by(service, post_data['created_by'])
+    validate_and_format_recipient(
+        send_to=post_data['filename'],
+        key_type=KEY_TYPE_NORMAL,
+        service=service,
+        notification_type=LETTER_TYPE,
+        allow_whitelisted_recipients=False,
+    )
 
     template = get_precompiled_letter_template(service.id)
     file_location = 'service-{}/{}.pdf'.format(service.id, post_data['file_id'])