BUILD: Improve error messages for optional dependencies Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

CONFIGURE: Inform about optional build dependencies Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

Secrets: m4 macros for jansson and http-parser Prepares autoconf for the new Secrets Provider dependencies Related: https://fedorahosted.org/sssd/ticket/2913 Signed-off-by: Christian Heimes <cheimes@redhat.com> Reviewed-by: Simo Sorce <simo@redhat.com>