Update eslint to v9, use new flat Apify eslint config

[jirimoravcik]

We should update eslint to v9 along with the new flat Apify eslint config that supports it.

See notion.so/apify/New-linting-and-formatting-configuration-across-Apify-0b62890892cd4b71b4fe2dee9291b4af?pvs=4#6152e086487441f6b974e6fbda9614be for a detailed guide.

[vladfrangu]

#765

[jirimoravcik]

Done in #765