Add context.Context parameter for Client.NewRequest interface

[cloudfly]

Proposal
add a context.Context parameter for method NewRequest in interface Client

---

current:

NewRequest(method, url string) *resty.Request

proposal:

NewRequest(ctx context.Context, method, url string) *resty.Request

So that, we can initialize the testy.Request with some information from the Context, such as injecting trace ID and JWT token in http header .

[alexmt]

thanks for proposal @cloudfly . It makes sense to me. WDYT, @devholic ?