Show the error body when status code is unknown

This can help to understand errors in the data better (for example
authentication, format errors).

exporters/otlp/otlplogs/otlplogshttp/client.go

@@ -347,7 +347,12 @@ func (d *httpClient) UploadLogs(ctx context.Context, protoLogs []*logspb.Resourc
  }
  return newResponseError(resp.Header)
  default:
- return fmt.Errorf("failed to send to %s: %s", request.URL, resp.Status)
+ buffer := make([]byte, 4096)
+ _, _ = resp.Body.Read(buffer)
+ if len(buffer) == 0 {
+ return fmt.Errorf("failed to send to %s: %s", request.URL, resp.Status)
+ }
+ return fmt.Errorf("failed to send to %s: %s\n%s", request.URL, resp.Status, buffer)
  }
  })
 }