Self-host the web app with Docker; publish the image to ghcr.io (#2033)

Thanks @rpromas.

packaging/docker/nginx.conf

@@ -0,0 +1,33 @@
+# The SolidCraft web app (packaging/docker/Dockerfile).
+#
+# Caching follows the app's update check (xtask/src/web_offline.rs): index.html, sw.js and
+# build.json must always be asked for again, or browsers keep an old build; Trunk's hashed
+# files (filehash = true) never change and are kept for a year.
+server {
+    listen 8080;
+    server_name _;
+    server_tokens off;
+    root /srv/solidcraft;
+    index index.html;
+
+    gzip on;
+    gzip_min_length 1024;
+    gzip_types application/wasm application/javascript text/css application/json application/manifest+json image/svg+xml font/ttf;
+
+    location / {
+        try_files $uri $uri/ =404;
+        add_header Cache-Control "no-cache" always;
+        add_header X-Content-Type-Options "nosniff" always;
+    }
+
+    location ~ "-[0-9a-f]{16}(_bg)?\.(js|wasm|css)$" {
+        add_header Cache-Control "public, max-age=31536000, immutable" always;
+        add_header X-Content-Type-Options "nosniff" always;
+    }
+
+    location ~ \.webmanifest$ {
+        default_type application/manifest+json;
+        add_header Cache-Control "no-cache" always;
+        add_header X-Content-Type-Options "nosniff" always;
+    }
+}