feat(httpx): implement optional body logging also on http error (#651)

1. we want optionally to log the body (we don't want to log the body
when we're fetching psiphon secrets or tor targets)

2. we want body logging to _also_ happen on error since this is quite
useful to debug possible errors when accessing the API

This diff adds the above functionality, which were previously
described in https://github.com/ooni/probe/issues/1951.

This diff also adds comprehensive testing.

internal/engine/probeservices/urls.go

@@ -28,7 +28,7 @@ func (c Client) FetchURLList(ctx context.Context, config model.OOAPIURLListConfi
 		query.Set("category_codes", strings.Join(config.Categories, ","))
 	}
 	var response urlListResult
-	err := c.APIClientTemplate.Build().GetJSONWithQuery(ctx,
+	err := c.APIClientTemplate.WithBodyLogging().Build().GetJSONWithQuery(ctx,
 		"/api/v1/test-list/urls", query, &response)
 	if err != nil {
 		return nil, err