Map LDAP attributes to claims

[roidelapluie]

the LDAP connector could get additional claims in its config, based on LDAP fields.

e.g:

{
  'available_claims':
  {
    'postal_code': 'postalCode'
  }
}

[ericchiang]

See #536 for some additional discussion around the LDAP connector. Overall, we should add a proposal on a good way to be more expressive with LDAP expressions.