[MOD-603][external] Add annotation file item_id and annotation id.

[whilefalse]

These fields are present in the darwin JSON v2 export, but they are not exposed by the relevant python types.

We need these for some upcoming work which reads darwin-py exports.

[linear]

MOD-603 [darwin-py] Expose item_id and annotation_id

Background

For calculating IOU matches in the pytorch-metrics script, we need to know these pieces of information, so that we can pass back the results to the backend in a nice format.

• dataset_item_id Required so that we know which item a set of matches belongs to
• annotation_id Required so we can send back the actual annotation ID matches, as opposed to just an index as we have now.

Solution

All of these things are currently available, it's just that they aren't exposed in the darwin-py datatypes.

• item_id is in the JSON, but not exposed on dt.AnnotationFile
• annotation_id is in the JSON, but not exposed on the dt.Annotation

The solution is to add new fields to the datatypes, and expose the relevant values:

• item_id - a new field on dt.AnnotationFile
• annotation_id - a new field on dt.Annotation

[Nathanjp91]

LGTM