fix(webservice): Forbid searching for attributes you cannot read

This makes sure that ACLs are respected when using ls method from
 webservice, with the following limitations:
It assumes that aclName == attributeName, otherwise the attribute is
 forbidden.
It assumes reading the main attribute is always authorized when the
 object can be seen.
It slows down the search in the case where you can read attribute in
 foo,bar but you search in bar.
All LDAP attributes can be used in the search filter.

issue #5704