[ldapfeed] make code compatible with ldap3>=2 * Some constants have been renamed. * Directly bind when data-cnx-dn/data-cnx-password are provided, some servers, including ours require this. * Use raise_exceptions=True to avoid ignored ldap errors * raise in case of failed anonymous bind * do not search for "dn" attribute because this raise an "invalid attribute" with new ldap3 versions * Password is now returned as bytes, so no longer need to encode them before crypt. * modification_date is now returned as a datetime object Co-Authored-By: Philippe Pepiot <philippe.pepiot@logilab.fr> Closes #16073071

[ldapfeed] use LDAP_SCOPES to find user-scope We already have LDAP_SCOPES dict defining possible scopes, this avoid possible code injection from config... Thus we can drop global variables already defined in LDAP_SCOPES since they are not used directly anymore.