ldap: Change ldap_user_certificate to userCertificate;binary
IPA and AD providers default to userCertificate;binary for the
ldap_user_certificate option. It will be good to default that value
also for the generic LDAP provider.
Resolves:
https://pagure.io/SSSD/sssd/issue/3499
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>