The config line for server.certfile is commented:
# Full path to the set of trusted CA certificates to verify your SSL certificate on Tableau Server in .pem format # example: 'c:\\certificates\\cacert.pem'
VizAlerts includes a .pem file in the \config folder already. Try pointing it to to that path instead. This is not the cert file itself, a cacert file is a collection of trusted certificate authority (CA) certificates. It's basically telling VizAlerts which certificate authorities it can trust. This is usually a pretty generic list, because they don't change often--that's why the file is included for you.
Thanks Matt Coles