Use ESLint "overrides" to configure based on availability of packages

[karlhorky]

The 1stG ESLint configs use overrides to enable different things in the config based on whether certain packages are available:

https://github.com/karlhorky/configs/blob/master/packages/eslint-config/overrides.js#L536

This would allow us to enable certain parts of the configure only if they are relevant eg:

1. React rules only if react package is available
2. Next.js rules only if next package is available
3. SafeQL only if the package is available