Add shared public edge (nginx + certbot)

One nginx owns host ports 80/443 for every project (Gitea, Musify) and
proxies by container name over infra-net and gitea_gitea; a certbot
service renews the Let's Encrypt certificates.

edge/snippets/acme-redirect.conf

@@ -0,0 +1,7 @@
+location /.well-known/acme-challenge/ {
+    root /var/www/certbot;
+}
+
+location / {
+    return 301 https://$host$request_uri;
+}