Improve instance storage size validation while attempting to restore the instance

Trove-API service should use datastore specific criteria/factor that used while validating the proposed storage size.
The issue comes from an ability to:
 - execute restore (if native restore tool allows to restore the data directly from stream, without saving it into the FS object);
 - save and execute restore (opposite situation to [1]).

Suggestion is to add the new conf value (for trove-api), that represents criteria/factor that help to define how much space does the backup requires to be saved and executed