[Feature]Add a default implementation of transfer fee and be able to specify priority fee

[YaakovHuang]

🚀 Feature

It is hoped that a default fee implementation can be provided when transfer credits, and the optional parameter priority fee can be added.

Motivation

The current transfer method must specify a fee, causing all the extra fees to be burned. This is a wasteful behavior. We hope that adding a default fee can ensure that the transaction can be confirmed normally. In addition, I want to increase my transfer speed, so I hope to provide a higher tip to speed up my transaction process. At this time, priority fee becomes very important, and I hope to add this option.