Convert swagger-client to ESM

[char0n]

Node.js world has moved to native ESM support some time ago. Wee need to get on this train to be able to used ESM or CommonJS packages. If we maintain status quo, we can only use older CommonJS packages.

Resources:

• https://nodejs.org/docs/latest-v16.x/api/esm.html
• https://nodejs.org/docs/latest-v16.x/api/packages.html

We already have explicit usage of file extension that was introduced in #2320.

We need to add "type": "module" to the package.json as well.

This change should be fully compatible so we should still be using older package fields like main or browser along with new exports.