Add support for Keep-Alive, Retry, HTTP/2, and createAndWait method

[BeeEyeVee]

Hello, and thanks for the great library!

We're experiencing occasional 502 Bad Gateway errors when using the CloudConvert Node.js library. We conduct over 220k conversions per month, and to help mitigate these issues, could you consider implementing the following features:

1. Keep-Alive for persistent connections.
2. Retry mechanism for handling transient network issues.
3. HTTP/2 support for improved performance.
   Additionally, it would be beneficial to have a method like createAndWait to simplify the process, instead of requiring separate calls to create and then wait.

Alternatively, allowing users to provide their own configured Axios instance would let us handle these settings ourselves.

Thank you for considering these enhancements!