Obtain TLS certificates for the Sandstorm instance

We'll need two TLS certificates:

1. *.storm.torproject.org — This one will need to be purchased.
2. A certificate which covers storm.torproject.org — This could be either the *.torproject.org cert (although I'm not entirely comfortable with having that key), or we could purchase a certificate for storm.torproject.org.

Related Tickets: #15241 (moved)