Support Datadog tracing

[Kroisse]

There may be cases where server applications communicate with each other via TGrid while using dd-trace for Datadog APM, or where web applications in browsers use Datadog RUM while communicating with servers through TGrid.

In typical HTTP communication, Datadog libraries like dd-trace either polyfill major libraries, or HTTP framework supports Datadog to enable service-to-service tracing. However, it seems that TGrid does not inherently support this functionality. Therefore, enabling Datadog tracing for TGrid could help users already using Datadog consider TGrid as a viable option.