CachingType type 
The type of caching in a data disk. 
KnownCachingType can be used interchangeably with CachingType,
this enum contains the known values that the service supports.
Known values supported by the service
None: Don't use host caching. 
ReadOnly: For workloads that only do read operations. 
ReadWrite: For workloads that do a balance of read and write operations.
type CachingType = string