Decide the content of `.eslintrc.cjs` and apply the new changes

https://codereview.qt-project.org/c/qt-labs/vscodeext/+/507911 introduces the `eslint` linter  and `.eslintrc.cjs`. `.eslintrc.cjs`  uses the default recommended configuration but it could be stricter. The team should decide the content of it. 

Example
```json

/* eslint-env node */
module.exports = {
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended-type-checked',
  ],
  plugins: ['@typescript-eslint'],
  parser: '@typescript-eslint/parser',
  parserOptions:

{     project: true,     tsconfigRootDir: __dirname,   }

,
  root: true,
};

```