KCM: Add a new back end that uses libsss_secrets directly
Add a new KCM back end that stores the ccaches in libsss_secrets
directly by using its API. The back end is only fake-async as all the
libsss_secrets functions are synchronous.
Related:
https://pagure.io/SSSD/sssd/issue/3685
Reviewed-by: Fabiano FidĂȘncio <fidencio@redhat.com>