Add http->http redirection for Matrix/Riot

Doing this means that matrix-nginx-proxy now starts
occupying port 80, which necessitates that
SSL renewal happens slightly differently.

roles/matrix-server/templates/nginx-conf.d/matrix-riot-web.conf.j2

@@ -1,3 +1,19 @@
+server {
+	listen 80;
+	server_name {{ hostname_riot }};
+
+	server_tokens off;
+
+	location /.well-known/acme-challenge {
+		default_type "text/plain";
+		alias /acmetool-certs/run/acme-challenge;
+	}
+
+	location / {
+		return 301 https://$http_host$request_uri;
+	}
+}
+
 server {
     listen 443 ssl http2;
     listen [::]:443 ssl http2;