Ability to generate globally unique values

[pflooky]

There is an option when generating values for fields to generate unique values. However, this is only done in the context of the current data generation session and does not take into account any existing data that may exist in the underlying data source. By default, we should generate unique values based on the existing data. It should be a flag that can be turned off as there will be a performance hit since we will have to pull in all the existing data.