Add an option such as 'carbon.update.storage.level' to configurate the storage level when updating data with 'carbon.update.persist.enable'='true'

[xm_zzc]

Hi all:
  when updating data, if 'carbon.update.persist.enable'='true', the dataset
in the method 'ProjectForUpdateCommand.processData' will be persisted, but
now it's storage level is MEMORY_AND_DISK, should it be set by user or not?
  if yes, I can implement it, and add an option such as
'carbon.update.storage.level' to configurate. 



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