(feature, typescript): Generarte API version scheme

[amckinney]

This adds support for generating an API version scheme in version.ts. Consider the following api.yml configuration:

version:
  header: X-API-Version
  default: "1.0.0"
  values:
    - "1.0.0-alpha"
    - "1.0.0-beta"
    - "1.0.0"

The following version.ts file is generated:

/**
 * This file was auto-generated by Fern from our API Definition.
 */

/** The version of the API, sent as the X-API-Version header. */
export type AcmeVersion = "1.0.0" | "2.0.0" | "latest";

If a default value is specified, it is set on every request but can be overridden in either the client-level Options or call-specific RequestOptions. If a default value is not specified, the value of the header is required on the generated Options.

An example call is shown below:

import { AcmeClient } from "acme";

const client = new AcmeClient({ apiKey: "YOUR_API_KEY", xApiVersion: "2.0.0" });
await client.users.create({
  firstName: "john",
  lastName: "doe"
});