[IO-1496][external] Expose the name, type, and edge_ids of Stage objects

[JBWilkie]

Problem

Stage objects currently don't expose their name, type, or edge_ids

Solution

Write Stage class properties to expose these fields

Changelog

Added the ability to access the name, type, and edge_ids of a Stage object

[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

[owencjones]

I've not approved yet, but this is good. If you DM me when you've considered all the stuff, then I'll approve.

[owencjones]

Not obligatory, but you could do this with a list comprehension, which are a bit faster, and worth getting used to.

    return [
        [edge.id, edge.source_stage_id, edge.target_stage_id]
        for edge in in self._element.edges
    ]

Optional, but consider it, and also have a think about listcomps in general.

[owencjones]

LGTM after PR changes