added server_names template file and updated redirectHTTPS to use it

availableSites/redirectHTTPS.conf

@@ -7,9 +7,8 @@ server {
     listen 80;
     listen [::]:80;
 
-    server_name server.domain.tld
-        subdomain.server.domain.tld
-        subdomain2.server.domain.tld;
+    # specify server name(s)
+    include /etc/nginx/snippets/server_names.conf;
 
     # redirect to properly formed HTTPS request
     return 301 https://$host$request_uri;

snippets/server_names.conf

@@ -0,0 +1,6 @@
+#######
+### NGINX configuration -- list of server names
+#######
+
+server_name
+    ;