azure-update: Add delete-all command to free up all ADU resources

This deletes all updates, device groups, device classes and associated
devices and deployments from the ADU instance. This is for housekeeping
of the ADU instance and must be used with caution, as it can interfere
with any ongoing CI runs that involve ADU.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>