Add capability for more complex filter for domain LDAP authentication

The LDAP authentication configuration makes the configuration to work with LDAP as simple as possible so there is no longer a need to understand a set of similarly named properties that have a complex interaction.

However there are some times more complex behaviour may be required when working with LDAP - we should support an advanced filter to locate the user in LDAP instead of only relying on the attribute which matches their username.