cubicweb #1382380 ldapuser: allow some additional filtering on which users are allowed to log on [validation pending]

on the ldap I need to connect to, in the same DN are users which are allowed to access the instance and users which are not. To tell them apart, I need to filter the list based on some other attributes (in this case memberOf with a wildcarded value). I therefore need to configure in the sources file an additional filter which will be used in the query by the ldapsource.

done in3.12.1
load left0.000
closed by<not specified>