feat: support setting http response status in functions

[jonbretman]

This makes it possible to set the HTTP response status from a function. This only has an effect on the HTTP JSON API, for GraphQL and JSON RPC the response status will always be 200.

Simple example

import { MyFunction, permissions } from "@teamkeel/sdk";

export default MyFunction(async (ctx) => {
  permissions.allow();

  const { response } = ctx;
  response.headers.set("Location", "https://some.url");
  response.status = 301;

  return null;
});

Request Headers

In this change I've also dropped the RequestHeaders class as I don't think it's necessary. Instead I've updated the types to be a Headers object with the mutating methods dropped.

[TejasQ]

Great! Let’s add this to the docs.

[jonbretman]

Great! Let’s add this to the docs.

Yep I'll get a docs PR together to go with this.

[davenewza]

👍