eslint@9 support (alias Flat config)

[jmeinlschmidt]

Current state:

• We are blocked by eslint-plugin-import (Support eslint v9 import-js/eslint-plugin-import#2948)

Resources:

• https://eslint.org/blog/2023/10/flat-config-rollout-plans/
• https://github.com/eslint/rfcs/tree/main/designs/2019-config-simplification
• 📈 Tracking: Flat Config support eslint/eslint#18093