Webpack: use filesystem cache for compilation (#643)

This allows to speed up webpack start. It went from 8s to 1s in my
laptop after the initial compilation.

By default, webpack uses memory cache, but it's deleted once the
container is shut down. Keeping the cache in the filesystem allows the
container to reuse the cached resources.

Author: humitos

webpack.config.mjs

@@ -55,6 +55,13 @@ export default (env, argv) => {
         },
       },
     },
+
+    // Use filesystem for cache instead memory (default) to be re-use the cache
+    // between Docker container starts/stops. This speeds up boot time a lot.
+    cache: {
+      type: is_production ? "memory" : "filesystem",
+    },
+
     module: {
       rules: [
         {