Proposal: Retry strategies

[speedfl]

Introduction

This proposal is an umbrella proposal for #1006 and #1007

To add more flexibility we could support different retry strategies:

client := resty.New().
    OnBeforeRequest(func(c *resty.Client, req *resty.Request) error {
        // Set your current token
        req.SetAuthToken(getCurrentToken())
        return nil
    }).
    WithRetryStrategy(resty.RertyOn(401).WithHook(func(r *resty.Response, err error) error {
        if r.StatusCode() == 401 {
            // Refresh token here
            retrun refreshToken() 
        })).
    WithRetryStrategy(resty.RertyOn(428).WithCount(3)).
    WithRetryStrategy(resty.Retry(func(r *resty.Response, err error) error {
         // custom logic
        return nil
        })).

Compared to #1006 and #1007 this issue could need more discussion so don't hesitate to challenge it