Allow to start operation with pre-defined root and parent ID

[SergeyKanzhelev]

StartOperaiton API doesn't support scenario when parent ID and root ID were received from different layer and we want to start operation with the existing parent and root ID.

Proposed change - allow StartOperaition to receive RequestTelemetry type as an argument

[pharring]

👍 to this, but also to allow passing the root ID as a raw value rather than as a RequestTelemetry.

[SergeyKanzhelev]

Why only root ID? Any significance for it?

[pharring]

Sure, parent ID too, optionally. It's possible the parent ID will be set via an initializer (e.g. in the case of a dependency in the context of an ASP.NET request).

i.e.

public static IOperationHolder<T> StartOperation<T>(this TelemetryClient telemetryClient, string operationName, string operationId = null, string operationParentId = null) where T : OperationTelemetry, new()
{
    ...
    operation.Telemetry.Start();

    if (!string.IsNullOrEmpty(operationId))
    {
        operation.Telemetry.Context.Operation.Id = operationId;
    }

    if (!string.IsNullOrEmpty(operationParentId))
    {
        operation.Telemetry.Context.Operation.ParentId = operationParentId;
    }

    ...

    telemetryClient.Initialize(operation.Telemetry);
    ...
}

I'll try to get a PR out for this later tonight.