Epic: Allow for large Segment rule values

**Is your feature request related to a problem? Please describe.**

Sometimes people want to provide a large (> 100) list of UUIDs or other identifiable datatype to target Identities. For various reasons (e.g. local evaluation mode with limited user context data in memory on the server), they might not be able to use traits.

**Describe the solution you'd like**

Allow the uploading of large lists of data that back segment rules like `IN`. This would be stored in a new type of data store such as Amazon S3 (or a new table in Postgres that accepts larger data values) and merged into memory of the flag engine at runtime.

We would need to design how the data is provided/ingested (via API, CSV upload etc) and what the performance considerations/limits of this approach might be.

**Describe alternatives you've considered**

Traits are the only way to achieve this sort of thing currently but sometimes disparate data makes them unworkable.