More detailed information on Dataset refresh failure email

The current email that 'alerts's the dataset owner of a failed scheduled refresh is nice. However, it doesn't contain the specific error information that is available in the Dataset refresh history and via the API.

This idea is to add the detailed reason for the failure, called the "Data source error"
e.g. Data source error: Scheduled refresh is disabled because at least one data source is missing credentials. To start the refresh again, go to this dataset's settings page and enter credentials for all data sources. Then reactivate scheduled refresh.