Round tripping of exported relationships do not restore relationship properties.

Relationships are exported like this:

```
{
"$relationshipId": "c8d57ca2-6cba-4c65-95da-dd17c97a102d",
"$sourceId": "mysourcetwin",
"$targetId": "mytargettwin",
"$relationshipName": "thisrelationshipisarelationship",
"myRelationshipStatus": "itscomplicated",
"$etag": "W/\"c431b939-f910-44e7-a682-f0def79d8b62\""
}
```

However, it looks like the importer is looking for relationship properties to be under a `$properties` node?

Start by tracing the relationship export and import paths in the repository and compare the exported shape with the importer’s expected property location. Reproduce a round trip using the relationship example from the issue; done means relationship properties such as myRelationshipStatus are preserved after export and import.

Written by the indexing model from the issue text.