OAuth refresh token support

[daigotanaka]

Currently, tap-rest-api doesn't fully support OAuth. It can customize the header, so if the developer can manually obtain the token and if it does not expire, the tap still works with the APIs with OAuth. That isn't the case for most services.
OAuth usually implements a refresh token with which we can obtain a new token after the older one expires.

It's probably possible to implement a generic OAuth refresh token flow. If we can achieve this, we just need to set a refresh token in the config, then run the flow to obtain the token.

I recently implemented such flow in PyPardotSF project, and I'm hoping to reuse some of the logic from it.