Move SSL certificates from /etc/pki/acmetool-certs to /matrix/ssl

Moving keeps everything in the /matrix directory, so that we
wouldn't contaminate anything else on the system or risk
clashing with something else.

Also retrieving certificates separately for the Riot and Matrix domains,
which should help in multiple ways:

- allows them to be very different (completely separate base domain..)

- allows for Riot to be disabled for the playbook some time later
  and still have the code not break

examples/host-vars.yml

@@ -5,7 +5,7 @@
 # an email notification there.
 #
 # Example value: someone@example.com
-host_specific_ssl_support_email: YOUR_EMAIL_ADDRESS_HERE
+host_specific_matrix_ssl_support_email: YOUR_EMAIL_ADDRESS_HERE
 
 # This is your bare domain name (`<your-domain`).
 #