[FEATURE REQUEST] Allow Users to Config Linode Auto Backup Schedule in Salt Cloud

[zliang-akamai]

Is your feature request related to a problem? Please describe.
A Linode VM now has an option to be created with auto backup enabled, but there is not anything to configures the schedule of the auto backup.

Describe the solution you'd like
Adding a function to allow users to configures the backup schedule.

Describe alternatives you've considered
An alternative way is to configures it during the VM creation, but that was not flexible enough and the Linode creation API doesn't support configuring the schedule neither.