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

@@ -348,7 +348,8 @@ 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)
+			body, _ := io.ReadAll(resp.Body)
+			return fmt.Errorf("failed to send to %s [%s]: %s", request.URL, body, resp.Status)
 		}
 	})
 }