ADD support for search_filter, precedence over search_attr

[ntavares]

The LDAP search_attr is very limiting, as it doesn't allow for more elaborate searches. One that is particularly useful is the support for the "disabled" status of an A/D entry. Adding this search_filter, which will have precedence over search_attr (for compatibility only, as it actually deprecates it), allows for searching users with a filter like, e.g.:

(&(objectClass=person)(&(!(userAccountControl:1.2.840.113556.1.4.803:=2))(sAMAccountName=%USERNAME%)))

Note: this is not the first attempt to get this into mainstream, see for instance:
https://www.freelists.org/post/racktables-users/how-can-I-use-filter-with-LDAP-auth,2

[infrastation]

Thank you for proposing this change, all new features will have to wait at least until release 0.22.0 is out (let's hope it will happen this year).

[ntavares]

Hi @infrastation! 0.22.0 is out, any chance to merge this?