(For Jintae or Gary) Add session level decision.

[mjouahri]

Purpose:

• Adds support for the session level decisions.

Technical overview:

• Updates data model to reflect the new decision.

Testing Plan

• Expanded and added unit tests and run them locally.

Deployment

• Publish to Maven
• Github release

[jintaekim20]

Mohammed, can you also update get_decisions and related code to include sessions? Also, please consider updating README.md and CHANGES.md.

Note: https://siftscience.com/developers/docs/python/decisions-api/decisions-list

[garylee1]

please also update CHANGES.md and version.py

[garylee1]

LGTM