Upgrade eslint dependencies to their new version

[milanholemans]

We are using eslint to notify us of coding patterns we shouldn't use. Currently, we are using eslint v8 while the latest version is eslint v9.
The new version has quite some breaking changes. The biggest is that we should convert our current eslintrc.cjs to a new format eslint.config.js. There is a migration guide on how to convert this config file: https://eslint.org/docs/latest/use/configure/migration-guide

Goal of this issue:
Let's try to upgrade our eslint dependencies to their latest version while keeping our current rules.