[IO-1496][external] Ensure edges are returned as WFEdgeCore objects

[JBWilkie]

Problem

In the original PR for IO-1496, edges were returned as a list of lists, with each item containing:

• edge_id
• source_stage_id
• target_stage_it

But, it makes more sense for the entire object to be returned in favour of the IDs within

Solution

Return WFEdgeCore objects instead of the IDs within them

Changelog

Ensure edges are returned as WFEdgeCore objects

[linear]

IO-1496 Stage is missing name, type, and edges

The Stage object doesn't expose name, type, or edges members.

Add these, as properties with loading if necessary.

Acceptance criteria

• Accessing name on Stage returns the name as a string
• Accessing type on Stage returns the type as an Enum/appropriate type
• Accessing edges on Stage returns the edges as a List