Signal an entity from an orchestration

[ahmedmuhsin]

Part of #141

Goal

Let an orchestrator signal an entity one way, with no result awaited, from task.OrchestrationContext.

Scope

• Add a signal entity method on the orchestration context that enqueues an operation for a target entity and returns without waiting.
• Support an optional scheduled time for delayed signals.

Reference

durabletask-dotnet TaskOrchestrationEntityFeature.SignalEntityAsync. Same operation message as a call, sent one way.

Depends on

The foundational entity runtime.