Register Multiple Files as a Model

In `azureml.core.Model.register()` we get the option of using `child_paths` to register multiple files as Model artifacts. However in `/azureml.core.run.Run.register_model()` we do not get any such options. Adding this option would be beneficial.

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#### Document Details

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* ID: 2e24ac95-7027-6a3c-81e6-f20cc4415219
* Version Independent ID: 9498cdc2-0d04-39a3-08ce-ef9ea8f2d153
* Content: [azureml.core.run.Run class - Azure Machine Learning Python](https://docs.microsoft.com/en-us/python/api/azureml-core/azureml.core.run.run?view=azure-ml-py#register-model-model-name--model-path-none--tags-none--properties-none--model-framework-none--model-framework-version-none--description-none--datasets-none--sample-input-dataset-none--sample-output-dataset-none--resource-configuration-none----kwargs-)
* Content Source: [AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.run.Run.yml](https://github.com/MicrosoftDocs/MachineLearning-Python-pr/blob/live/AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.run.Run.yml)
* Service: **machine-learning**
* Sub-service: **core**
* GitHub Login: @DebFro
* Microsoft Alias: **debfro**