settings: Import LDAP settings in prod_settings_template.

Currently users that try to deploy Zulip through docker has errors
because LDAP group search configuration can't be automated.

Reverts a hunk of f5197518a9.

tools/linter_lib/pyflakes.py

@@ -7,6 +7,8 @@ from zulint.linters import run_pyflakes
 def check_pyflakes(files: List[str], options: argparse.Namespace) -> bool:
     suppress_patterns = [
         ("scripts/lib/pythonrc.py", "imported but unused"),
+        # LDAP imports are necessary for docker-zulip.
+        ("zproject/prod_settings_template.py", "imported but unused"),
         # Our ipython startup pythonrc file intentionally imports *
         ("scripts/lib/pythonrc.py", " import *' used; unable to detect undefined names"),
         (

zproject/prod_settings_template.py

@@ -155,7 +155,7 @@ AUTHENTICATION_BACKENDS: Tuple[str, ...] = (
 ## optionally using LDAP as an authentication mechanism.
 
 import ldap
-from django_auth_ldap.config import LDAPSearch
+from django_auth_ldap.config import GroupOfNamesType, LDAPGroupQuery, LDAPSearch
 
 ## Connecting to the LDAP server.
 ##