Pipe protocol: Introduce handshaking with orchestrator

[Youssef1313]

Today, test host controllers and test hosts do handshake in the pipe protocol used for dotnet test. We should probably also make the orchestrator handshake as well, potentially with a "reason"/"feature" property. Today, the only known "feature" is "retry".

It might be also useful to add timestamps to all messages sent in the protocol.

[Youssef1313]

Note: when running --help, we should also handshake.