Trial new ESLint "flat configs" system

[thibaudcolas]

Config dependencies’ management has finally been improved (eslint/eslint#3458), with a preview release in a recent ESLint v8 minor release:

• https://eslint.org/blog/2022/08/new-config-system-part-1/
• https://eslint.org/blog/2022/08/new-config-system-part-2/
• https://eslint.org/blog/2022/08/new-config-system-part-3/

Switching over to "flat configs" will greatly simplify the setup for our projects, so we should give it a go and potentially migrate over to it shortly.