Add support for segment management in API client (App and Track)

[fantomiks]

Overview

This PR introduces new functionality to handle segments in the API client. It includes the following features:

• Create, list, retrieve, and delete segments
• Manage segment dependencies and customer counts
• Add and remove people from segments
• Enum types for segment state and segment type

Changes

1. Added methods to manage segments (CreateSegment, ListSegments, GetSegment, DeleteSegment).
2. Added methods to handle customers in segments (AddPeopleToSegment, RemovePeopleFromSegment).
3. Introduced new data structures: Segment, SegmentState, SegmentType, and associated types.

Why this change is needed

These additions expand the capabilities of the API client by enabling users to manage segments directly, which was previously not possible.

Testing

• Added unit tests for all new functions.
• Verified segment management endpoints with the API using real data.
• Confirmed that all existing tests pass.