Handle 429 Too Many Requests status

[techpeace]

Adds support for HTTP 429 Too Many Requests status.

[techpeace]

Howdy! Thanks for the library 🙌

I ran into the issue raised in #38 myself recently:

Failed to get image for https://www.bleepingcomputer.com/news/security/healthcare-services-group-data-breach-impacts-624-000-people: {
  error: true,
  result: {
    success: false,
    requestUrl: 'https://www.bleepingcomputer.com/news/security/healthcare-services-group-data-breach-impacts-624-000-people',
    error: 'Server has returned a 400/500 error code',
    errorDetails: Error: Server has returned a 400/500 error code

I found I had to add some logging to request.ts in order to track down the actual issue (the 429, in my case).

Would it make sense to surface any part of the response in the error object, in addition to errorDetails? I realize status and statusText could be duplicative if it's caught by the case statement.