LDAP auth: introduce config option 'ldap_groups_attribute'

This attribute is supposed to hold the group membership information
if the config option 'ldap_load_groups' is True.
If not given, it defaults to 'memberOf' for Active Directory.

Introducing this options allows one to use radicale's LDAP auth with groups
even on LDAP servers that keep their group memberships in a different attribute
than 'memberOf', e.g. Novell eDirectory which uses 'groupMembership'.

config

@@ -89,6 +89,9 @@
 # If the ldap groups of the user need to be loaded
 #ldap_load_groups = True
 
+# the attribute to read the group memberships from in the user's LDAP entry if ldap_load_groups is True.
+#ldap_groups_attribute = memberOf
+
 # The filter to find the DN of the user. This filter must contain a python-style placeholder for the login
 #ldap_filter = (&(objectClass=person)(uid={0}))