update eslint to v9

[mob8607]

This includes many breaking changes. The biggest one is the change from .eslintrc to a flat config file (eslint.config.js).

Also all the plugins that are used need to support eslint v9 as well.

Known Missing Support on May, 8th:

• Support ESLint v9 vuejs/eslint-config-typescript#76
• https://github.com/valantic/eslint-config-valantic

Blog: https://eslint.org/blog/2024/04/eslint-v9.0.0-released/

There is a branch where I started with a refactoring:

feature/374_eslint-update

Weiters:

• Evaluieren ob wir air-bnb weiterhin als unsere basis verwenden.
  • Eventuelle ersatz: https://github.com/sindresorhus/eslint-plugin-unicorn/blob/main/package.json
  • https://www.npmjs.com/package/eslint-plugin-sonarjs