Change superagent for the fetch api?

https://github.com/swagger-api/swagger-codegen/blob/068b1ebcb7b04a48ad38f1cadd24bb3810c9f1ab/modules/swagger-codegen/src/main/resources/Javascript/es6/ApiClient.mustache#L2-L3

Reason for switching

• superagent use xhr instead of fetch and therefor don't work in service worker
  • fetch also has streaming support (unlike xhr)
• Deno and Browser have fetch built in so no extra dependency, for node you could import eg node-fetch
  • there is a hot topic in bringing in the fetch api or similar functionality into node
• fewer dependencies -> more lightweight
• querystring is legacy
  • The URLsearchParam uses a more selective and fine grained approach to selecting encoded characters than that used by the Legacy API.
  • querystring.parse is depricated since v11
  • URLSearchParams is available in more environments without the need of any dependencies
  • querystring will mix the value between string and arrays giving you an inconsistent api

Start with modules/swagger-codegen/src/main/resources/Javascript/es6/ApiClient.mustache at lines 2-3 and inspect how the generated client uses superagent and querystring. Compare the required browser, service-worker, Deno, and Node environments with the proposed Fetch and URLSearchParams APIs. Done means the generated JavaScript client no longer depends on the named legacy components while retaining its existing request behavior.