Enable passing custom data on pipeline instantiation

[anthonypuppo]

The DataPipeline.CustomData property currently only supports inter-handler communication. It would be useful to be able to "bootstrap" with data from the caller (telemetry correlation identifiers, etc).

Proposal, add a Dictionary<string, object>? customPipelineData argument to the necessary orchestrator/memory methods which sets DataPipeline.CustomData before the initial pipeline file write.

BaseOrchestrator.ImportDocumentAsync could change to something like:

public async Task<string> ImportDocumentAsync(string index, DocumentUploadRequest uploadRequest, Dictionary<string, object>? customPipelineData = null, CancellationToken cancellationToken = default)
{
    this.Log.LogInformation("Queueing upload of {0} files for further processing [request {1}]", uploadRequest.Files.Count, uploadRequest.DocumentId);

    var pipeline = this.PrepareNewDocumentUpload(
        index: index,
        documentId: uploadRequest.DocumentId,
        uploadRequest.Tags,
        uploadRequest.Files);

    if (customPipelineData is { Count: > 0 })
    {
        pipeline.CustomData = customPipelineData;
    }
    
    // ...
}

I can create a PR if this is a valuable addition.

[dluc]

Here it is, handlers now can receive in input custom data: #673