sysdb: add certmap related calls
    
    Add sysdb calls to write and read data for the certificate mapping
    library to the cache.
    
    Related to https://pagure.io/SSSD/sssd/issue/3050
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>