modules: services: matrix: SSL only for server

This is a requirement anyway for homeservers, and the `forceSSL` option
tried to create a redirect for non-SSL traffic, except the `listen`
option only provided SSL endpoints anyway, so this resulted in
additional rules in the nginx config looking like this:

```nginx
server {
        server_name matrix.belanyi.fr ;
        location /.well-known/acme-challenge {
                root /var/lib/acme/acme-challenge;
                auth_basic off;
        }
        location / {
                return 301 https://$host$request_uri;
        }
}
```

modules/services/matrix.nix

@@ -121,7 +121,7 @@ in
 
     services.nginx.virtualHosts = {
       "matrix.${domain}" = {
-        forceSSL = true;
+        onlySSL = true;
         useACMEHost = domain;
 
         locations =
@@ -149,7 +149,7 @@ in
 
       # same as above, but listening on the federation port
       "matrix.${domain}_federation" = rec {
-        forceSSL = true;
+        onlySSL = true;
         serverName = "matrix.${domain}";
         useACMEHost = domain;