Go for a more generic js bundling architecture

* Don't tie the output name to webpack itself
* Don't call js bundling webpack in python code
* Make the doc more generic about js bundling

core/static/bundled/alpine-index.js

@@ -0,0 +1,7 @@
+import Alpine from "alpinejs";
+
+window.Alpine = Alpine;
+
+window.addEventListener("DOMContentLoaded", () => {
+  Alpine.start();
+});