Fix eslint config

[tjzel]

Summary

Because we use ESlint rules that require a parses, proper amendments to the .eslintrc.js had to be made. Because of that we can also finally extend main .eslintrc.js config in sub-directiories.

You can read more here.

As a note, I recommend eslint --print-config <file> to debug if the rules are actually extended etc.

Test plan

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