client logs query parameters, which can leak secrets

There are several places where `url.URL` is used in a log or error, for example:

via logs:
https://github.com/hashicorp/go-retryablehttp/blob/571a88bc9c3b7c64575f0e9b0f646af1510f2c76/client.go#L597

via returned error:
https://github.com/hashicorp/go-retryablehttp/blob/571a88bc9c3b7c64575f0e9b0f646af1510f2c76/client.go#L751

While the former can be mitigated by setting a `nil` logger on client instantiation, users of the client have to deal with potential query param / data leaks through errors.

We would like to see either a removal of query params entirely, or an option to disable full query param reporting. We could replace instances of `url.URL` with a few options:

```
# Option 1, build URL w/o query params
cleanURL := url.Scheme + "://" + url.Host + url.Path

# Option 2, truncate query params
cleanURL := strings.Split(url.URL, "?")[0]
```