Migrate ESLint config to flat config format

Author: mao-sz

.eslintignore

@@ -0,0 +1,13 @@
+const js = require("@eslint/js");
+const globals = require("globals");
+const { defineConfig, globalIgnores } = require("eslint/config");
+
+module.exports = defineConfig([
+  globalIgnores(["archive/"]),
+  {
+    files: ["generators/**/*.js", "**/*.spec.js", "**/*-solution.js", "*.js"],
+    plugins: { js },
+    extends: ["js/recommended"],
+    languageOptions: { globals: { ...globals.node, ...globals.jest } },
+  },
+]);