ZonalUpdateMode type  
Indicates the update mode for Cross Az clusters. 
KnownZonalUpdateMode can be used interchangeably with ZonalUpdateMode,
this enum contains the known values that the service supports.
Known values supported by the service
Standard: The cluster will use 5 upgrade domains for Cross Az Node types. 
Fast: The cluster will use a maximum of 3 upgrade domains per zone instead of 5 for Cross Az Node types for faster deployments.
type ZonalUpdateMode = string