Support for custom tags

Is this where we make feature requests for the SDK?

Can we add an argument for custom tags to be supplied during the cluster creation (also in the DatabricksStep method) so these tags can be propagated to the Azure resources for cost allocation and management?

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* ID: 9863b70a-fd6f-8cf1-0e45-7f21f6129f0f
* Version Independent ID: b22101ec-f43e-9a80-7189-1ff59626cb59
* Content: [azureml.core.databricks.DatabricksCluster class - Azure Machine Learning Python](https://docs.microsoft.com/en-us/python/api/azureml-core/azureml.core.databricks.databrickscluster?view=azure-ml-py)
* Content Source: [AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.databricks.DatabricksCluster.yml](https://github.com/MicrosoftDocs/MachineLearning-Python-pr/blob/live/AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.core.databricks.DatabricksCluster.yml)
* Service: **machine-learning**
* Sub-service: **core**
* GitHub Login: @DebFro
* Microsoft Alias: **debfro**