Infrstructure: Adding ESLint

[GregOnNet]

Hey there,

while working on #27, I accidently introduced a shadowed variable:

func(results: unknown) {
  const promises = [];

  Promise.all(promises).then(results) => {
    // ...
    results[key]... // 💥 I meant results of func not the local results ...
  }
} 

This failure caused a mistake.

If we introduce eslint, problemes like this are directly marked in the IDE.

What about, setting up eslint?

Resources
typescript-eslint.io/getting-started

[GregOnNet]

[GregOnNet]

Copied the answer from the original issue.