Migrate to native fetch from superagent

[Andrii Kostenko]

1. Superagent is a monster with tons of dependencies
2. It is barely supported
3. transitional dependency of superagent (formidable) has critical vulnerability and now npm barks about critical vulnerability in every package, which uses zerossl

[Adam K Dean]

Thanks for this + PR.

We're going to review this and decide whether the best route is to replace superagent (as per your PR) or update it.