[FEATURE_REQUEST] Provide guidance on how to obtain a subscription id in 11_exploring_hyperparameters_on_azureml notebook

[mawah]

Description

Users need to modify the third code cell to specific a subscription id and the names that will be used for creating a resource group, workspace, etc. Some guidance within the notebook on how to obtain these values and fill in the strings would be helpful.

It would also be nice to throw an error in this code cell if users forget to fill in the values, so that users don't encounter a cryptic error from the call to get_or_create_workspace() later on.

Expected behavior with the suggested feature

Users who forget to fill in the string values in this code cell are alerted to the issue by an error message from this code cell. Novice users receive some guidance on how to obtain their Azure subscription id without having to reference other notebooks.

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