SQL Data Warehouse: User-defined maintenance scheduling

[Azure SQL Data Warehouse](https://docs.microsoft.com/en-us/azure/sql-data-warehouse/maintenance-scheduling) maintenance scheduling is now in preview. This is a new feature that seamlessly integrates the Azure Service Health planned maintenance notifications with Resource Health monitor services. Maintenance scheduling allows customers to plan around the scheduled maintenance events that the Azure SQL Data warehouse service uses to roll out new features, upgrades and patches. [Learn more](https://docs.microsoft.com/en-us/azure/sql-data-warehouse/maintenance-scheduling). * Azure Synapse Analytics * Services