mailman3: fix search

roles/mailman3/templates/settings.py.j2

@@ -47,3 +47,10 @@ SERVER_EMAIL = 'root@{{ lists_domain }}'
 
 POSTORIUS_TEMPLATE_BASE_URL = 'http://localhost'
 HYPERKITTY_ALLOW_WEB_POSTING = False
+
+HAYSTACK_CONNECTIONS = {
+    'default': {
+        'ENGINE': 'haystack.backends.whoosh_backend.WhooshEngine',
+        'PATH': '/var/lib/mailman-web/fulltext_index'
+    }
+}