Add openssh ldap pubkey support compatible with openssh-lpk

[runleveldev]

See https://github.com/jirutka/ssh-ldap-pubkey/blob/master/etc/openssh-lpk.schema

1. Update the LdapUser object to take an optional sshpublickey field

   LDAPServer/npm/src/utils/ldapUtils.js

   Line 7 in 767bb26

   * @typedef {Object} LdapUser

2. In the createLdapEntry function, if the sshpublickey field has been provided, it should be included in the LDAP response using the sshPublicKey attribute AND the objectClass array should have the ldapPublicKey appended.
3. New tests should be added including an integration test to ensure sssd with the AuthorizedKeysCommand /usr/bin/sss_ssh_authorizedkeys works as expected