add "from datetime import timedelta" line to wikiconfig; fixes moinwi…

…ki#1754

needed if wiki admin changes PERMANENT_SESSION_LIFETIME value
in wikiconfig.py.

>>>> manual copy of src/moin/config/wikiconfig.py over wikiconfig.py
required afer applying this patch

src/moin/config/wikiconfig.py

@@ -263,6 +263,7 @@ class Config(DefaultConfig):
 SESSION_COOKIE_HTTPONLY = True  # flask default is True
 SESSION_COOKIE_SAMESITE = "Lax"  # flask default is None
 # SESSION_COOKIE_NAME = 'session'
+# from datetime import timedelta  # next line requires this
 # PERMANENT_SESSION_LIFETIME = timedelta(days=31)
 # USE_X_SENDFILE = False
 # LOGGER_NAME = 'MoinMoin'