Support for ESLint's New Flat Configs

[tthornton3-chwy]

Available in newer versions of ESLint, and will be required in the future, there's a new configuration structure! You can find the context here: https://eslint.org/docs/latest/use/configure/configuration-files-new

While there does exist a utility (https://www.raulmelo.me/en/blog/migration-eslint-to-flat-config#official-utility-for-the-rescue) to convert between the two, it's a bit gross, and I didn't have much luck with it properly loading in the overrides.

We were using the https://github.com/google/gts#working-with-eslint aspect of this in a few of our repos! And I wound up essentially making my own using the same rules over in the new style.

Thanks for your time, and your support!

[tonycoco]

Happy to review a PR if someone wants to convert the existing RC to the new config style.

[jdugas]

Eslint has deprecated the use of config files that are not the new flat configs. config files deprecated

[tonycoco]

Working on the flat config for the next release

[tthornton3-chwy]

Thanks Tony :) Happy to test anything then. I've moved away from it for now, but I can make sure to come back and help look at it.

[tonycoco]

#886 Gets pretty close but we will need to wait for Node 14/16 deprecation to bump ESlint versions. Might be able to do it without that package change. I'll take a better look as soon as I have time.