Set baseUrl per request

[RobinClowers]

Description

My app has an API that is per tenant, so I end up having to create a client every time I need to call the API, since the baseUrl varies.

Proposal

Ideally it would be as simple as:

client.GET("/api/region", {
  baseUrl: "https://api.example.com",
})

Checklist

• I’m willing to open a PR for this (see CONTRIBUTING.md)