server: Add modifyTimestamp and pwdChangedTime attributes (#1265)

Add a modifyTimestamp attribute to LDAP entries for users and groups, and expose pwdChangedTime for users.
These attributes let clients track when an entry (or its password) was last changed.

 -  modifyTimestamp is a server-maintained attribute that updates on any write to user or group entries, including membership changes (on the group side).

 -  pwdChangedTime is set when a user’s password is created or changed.

crates/ldap/src/handler.rs

@@ -398,6 +398,7 @@ pub mod tests {
                     creation_date: chrono::Utc.timestamp_opt(42, 42).unwrap().naive_utc(),
                     uuid: uuid!("a1a2a3a4b1b2c1c2d1d2d3d4d5d6d7d8"),
                     attributes: Vec::new(),
+                    modified_date: chrono::Utc.timestamp_opt(42, 42).unwrap().naive_utc(),
                 });
                 Ok(set)
             });