Add zipfian distribution option to vary value size for continuous ingest

[DomGarguilo]

This PR adds an optional component to the value created in continuous ingest. A random portion of data will be inserted into the value whose size is determined via a zipfian distribution.

The motivation behind this is to add optional variance to the sizes of values that are inserted via continuous ingest. Zipfian distribution was selected since it tends to correspond to the distribution of real-world events.