feat: Support OAuth access token

[koba04]

Motivation

Kintone has OAuth access token support, but rest-api-client doesn't support yet.
So we want rest-api-client to accept OAuth access token.

ref. #64

Overview

This PR make rest-api-token to be able to accept OAuth token at its constructor.

// This interface hasn't fixed so we might change the interface
const client = new KintoneRestAPIClient({
  baseUrl: "https://example.cybozu.com",
  auth: {
    oauthToken: process.env.KINTONE_OAUTH_TOKEN
  }
});