provision: delay initialization of secrets until provision time

when we create the DO 1-click image, the key also gets snapshotted.

https://community.letsencrypt.org/t/receiving-expiration-emails-for-dozens-of-domains/165441

src/nginxconfig.ejs

@@ -87,7 +87,10 @@ server {
     ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-SHA256;
     ssl_prefer_server_ciphers off;
 
+    # dhparams is generated only after dns setup
+<% if (endpoint !== 'ip' && endpoint !== 'setup') { -%>
     ssl_dhparam /home/yellowtent/platformdata/dhparams.pem;
+<% } -%>
     add_header Strict-Transport-Security "max-age=63072000";
 
     <% if ( ocsp ) { -%>