Add a configuration file entry to handle and expired SSL certificate

Add an additional line the configuration file identifying how an expired SSL certificate for the site is handled. If the SSL certificate is valid (other than being expired), the "External Accessibility Check" could then take that setting into account and flag the check accordingly, i.e., it could - for instance - use a status of "Expired" rather than "Failed" and mark that line with a yellow vertical bar rather than a red one.