chore(deps): update dependency eslint to v9 (#11601)

* chore(deps): update dependency eslint to v9

* chore: migrate to eslint flat config files

---------

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Daniel Dietzler <mail@ddietzler.dev>

server/eslint.config.mjs

@@ -0,0 +1,80 @@
+import { FlatCompat } from '@eslint/eslintrc';
+import js from '@eslint/js';
+import typescriptEslint from '@typescript-eslint/eslint-plugin';
+import tsParser from '@typescript-eslint/parser';
+import globals from 'globals';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = path.dirname(__filename);
+const compat = new FlatCompat({
+  baseDirectory: __dirname,
+  recommendedConfig: js.configs.recommended,
+  allConfig: js.configs.all,
+});
+
+export default [
+  {
+    ignores: ['eslint.config.mjs'],
+  },
+  ...compat.extends(
+    'plugin:@typescript-eslint/recommended',
+    'plugin:prettier/recommended',
+    'plugin:unicorn/recommended',
+  ),
+  {
+    plugins: {
+      '@typescript-eslint': typescriptEslint,
+    },
+
+    languageOptions: {
+      globals: {
+        ...globals.node,
+      },
+
+      parser: tsParser,
+      ecmaVersion: 5,
+      sourceType: 'module',
+
+      parserOptions: {
+        project: 'tsconfig.json',
+        tsconfigRootDir: __dirname,
+      },
+    },
+
+    rules: {
+      '@typescript-eslint/interface-name-prefix': 'off',
+      '@typescript-eslint/explicit-function-return-type': 'off',
+      '@typescript-eslint/explicit-module-boundary-types': 'off',
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-floating-promises': 'error',
+      'unicorn/prevent-abbreviations': 'off',
+      'unicorn/filename-case': 'off',
+      'unicorn/no-null': 'off',
+      'unicorn/prefer-top-level-await': 'off',
+      'unicorn/prefer-event-target': 'off',
+      'unicorn/no-thenable': 'off',
+      'unicorn/import-style': 'off',
+      'unicorn/prefer-structured-clone': 'off',
+      '@typescript-eslint/await-thenable': 'error',
+      '@typescript-eslint/no-misused-promises': 'error',
+      'require-await': 'off',
+      '@typescript-eslint/require-await': 'error',
+      curly: 2,
+      'prettier/prettier': 0,
+
+      'no-restricted-imports': [
+        'error',
+        {
+          patterns: [
+            {
+              group: ['.*'],
+              message: 'Relative imports are not allowed.',
+            },
+          ],
+        },
+      ],
+    },
+  },
+];