Allow to overwrite ONNX Model Shape and multiple input and outputs

I was unable to run DB_TD500_resnet50.onnx model (https://docs.opencv.org/4.x/d4/d43/tutorial_dnn_text_spotting.html) using OnnxModel as it was throwing following error - Length of memory (1625088) must match product of dimensions (3).

The only way to fix it was to duplicate OnnxModel locally and pass the correct shapeDictionary when applying ONNX Model

this.context.Transforms.ApplyOnnxModel(
      modelFile: configuration.ModelFileName,
      outputColumnNames: new[] { configuration.OutputVectorName },
      inputColumnNames: new[] { configuration.InputVectorName },
      gpuDeviceId: configuration.GpuDeviceId,
      shapeDictionary: new Dictionary<string, int[]>()
          {
             { "input", new[] { 1, 3, 736, 736} }
          });

Request is to allow overriding shapeDictionary when creating OnnxModel. This overriding requirement also exist to run FasterRCNN model https://github.com/dotnet/machinelearning/pull/3963

Start by tracing the OnnxModel creation path and the ApplyOnnxModel call described in the issue, including how shapeDictionary is currently passed. Reproduce the DB_TD500_resnet50.onnx failure and compare it with the FasterRCNN requirement. Done means callers can override the model shape and support multiple inputs and outputs without duplicating OnnxModel.