SnapshotException (status_code: 403)

Hi,

I have encountered SnapshotException with status code 403. It turns out that I have a read permission but not write permission for the subscription I was trying to submit my job to. It would be better if the error message was more informative.

This is the current error message
```
raise SnapshotException(get_http_exception_response_string(response))
azureml.exceptions._azureml_exception.SnapshotException: SnapshotException:
Message: {
"status_code": 403,
"url": "..."
}
InnerException None
ErrorResponse
{
"error": {
"message": "{\n \"status_code\": 403,\n \"url\": \"...\"\n}"
}
}
```

I think a better error message would be
```
Please make sure that you have write permission to subscription XYZ.
```

It might also be a good idea to document here what the typical causes for different status codes are.

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* ID: 9c023d0b-94c0-8b80-3a43-e0d5beb2eefb
* Version Independent ID: 22714d0e-0f49-7264-5329-7c7b3e163d2d
* Content: [azureml.exceptions.SnapshotException class - Azure Machine Learning Python](https://docs.microsoft.com/en-us/python/api/azureml-core/azureml.exceptions.snapshotexception?view=azure-ml-py)
* Content Source: [AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.exceptions.SnapshotException.yml](https://github.com/MicrosoftDocs/MachineLearning-Python-pr/blob/live/AzureML-Docset/stable/docs-ref-autogen/azureml-core/azureml.exceptions.SnapshotException.yml)
* Service: **machine-learning**
* Sub-service: **core**
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* Microsoft Alias: **debfro**