Lack of support for flat config (default starting in ESLint v9.0.0)

[artus9033]

Environment

ESLint $\geqslant 9.0.0$
@callstack/eslint-config ^14.2.0

Description

The config does not work since it does not use flat config, which is the default since ESLint v9.0.0.

It can be worked around by setting the env var ESLINT_USE_FLAT_CONFIG=false, yet it would be good to support the new format, also having backwards-compatible (eslintrc-style) configuration exports.

Reproducible Demo

Upgrade ESLint to $\geqslant 9.0.0$ in any project using eslint-config-callstack and run ESLint.

[marcinkornek]

@artus9033 library supports ESLint flat config since version 15.0.0 https://github.com/callstack/eslint-config-callstack/releases/tag/v15.0.0

[artus9033]

Hey, thanks @marcinkornek & @thymikee ! I must've forgotten about tagging this one in the PR.