Bump eslint from 8.57.0 to 9.0.0 in /src/backend (#6979)

* Bump eslint from 8.57.0 to 9.0.0 in /src/backend

Bumps [eslint](https://github.com/eslint/eslint) from 8.57.0 to 9.0.0.
- [Release notes](https://github.com/eslint/eslint/releases)
- [Changelog](https://github.com/eslint/eslint/blob/main/CHANGELOG.md)
- [Commits](https://github.com/eslint/eslint/compare/v8.57.0...v9.0.0)

---
updated-dependencies:
- dependency-name: eslint
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* rename configs

* rewrite the config for 9.0

* rename again

* fix packages

* fix config for new style

* disable reportUnusedDisableDirectives for now

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Matthias Mair <code@mjmair.com>

src/backend/eslint.config.js

@@ -0,0 +1,38 @@
+// eslint.config.js
+import js from "@eslint/js";
+import globals from "globals";
+
+export default [
+  js.configs.recommended,
+  {
+    languageOptions: {
+      ecmaVersion: 12,
+      sourceType: "module",
+      globals: {
+        ...globals.browser,
+        ...globals.es2021,
+        ...globals.jquery,
+      }
+    },
+    rules: {
+      "no-var": "off",
+      "guard-for-in": "off",
+      "no-trailing-spaces": "off",
+      "camelcase": "off",
+      "padded-blocks": "off",
+      "prefer-const": "off",
+      "max-len": "off",
+      "require-jsdoc": "off",
+      "valid-jsdoc": "off",
+      "no-multiple-empty-lines": "off",
+      "comma-dangle": "off",
+      "no-unused-vars": "off",
+      "no-useless-escape": "off",
+      "prefer-spread": "off",
+      "indent": ["error", 4]
+    },
+    linterOptions: {
+      reportUnusedDisableDirectives: "off"
+  }
+  }
+];