DnnCatalog methods should use a public Options class

[eerhardt]

The two methods in DnnCatalog:

machinelearning/src/Microsoft.ML.Dnn/DnnCatalog.cs

Lines 49 to 63 in c9f616f

	public static DnnRetrainEstimator RetrainDnnModel(
	this ModelOperationsCatalog catalog,
	string[] outputColumnNames,
	string[] inputColumnNames,
	string labelColumnName,
	string dnnLabel,
	string optimizationOperation,
	string modelPath,
	int epoch = 10,
	int batchSize = 20,
	string lossOperation = null,
	string metricOperation = null,
	string learningRateOperation = null,
	float learningRate = 0.01f,
	bool addBatchDimensionInput = false)

and

machinelearning/src/Microsoft.ML.Dnn/DnnCatalog.cs

Lines 120 to 143 in c9f616f

	public static ImageClassificationEstimator ImageClassification(
	this ModelOperationsCatalog catalog,
	string featuresColumnName,
	string labelColumnName,
	string scoreColumnName = "Score",
	string predictedLabelColumnName = "PredictedLabel",
	Architecture arch = Architecture.InceptionV3,
	int epoch = 100,
	int batchSize = 10,
	float learningRate = 0.01f,
	bool disableEarlyStopping = false,
	EarlyStopping earlyStopping = null,
	ImageClassificationMetricsCallback metricsCallback = null,
	int statisticFrequency = 1,
	DnnFramework framework = DnnFramework.Tensorflow,
	string modelSavePath = null,
	string finalModelPrefix = "custom_retrained_model_based_on_",
	IDataView validationSet = null,
	bool testOnTrainSet = true,
	bool reuseTrainSetBottleneckCachedValues = false,
	bool reuseValidationSetBottleneckCachedValues = false,
	string trainSetBottleneckCachedValuesFilePath = "trainSetBottleneckFile.csv",
	string validationSetBottleneckCachedValuesFilePath = "validationSetBottleneckFile.csv"
	)

have a lot of optional parameters, and users may get confused on which ones are important, and which aren't.

I've seen comments from @terrajobst in the past saying:

In UX studies we have seen that many developers struggle with methods that have many optional arguments.

In ML.NET, the pattern we have established is that we have 2 overloads:

1. An overload that takes the required parameters, and optionally the most important/common parameters to a method.
2. An overload that takes an Options object, which contains all the options to the method - simple and advanced.

We should follow this pattern with these DNN APIs as well. See the discussions and related PRs to #1798.

/cc @ebarsoumMS @codemzs

[codemzs]

@eerhardt We are aware and already tracking this issue and it will be implemented before we go GA.

[ashbhandare]

I will be looking into this.

[codemzs]

Thanks @ashbhandare