add demo on grpc dialtesting

[coanor]

No description provided.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ axingGo
❌ coanor
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[coanor]

/lgtm