NIAD-972: Map test groups

[andrewwa-kainos]

Description

Observations that group test results reference them with "has-member". Test results reference their groups (if any) with an unqualified relation. The patient, performer and specimen are now also linked, which needed some refactoring of the mappers.

Jira Ticket

Parent: https://gpitbjss.atlassian.net/browse/NIAD-972 Sub-task: https://gpitbjss.atlassian.net/browse/NIAD-1144

Checklist

These are items (excluding GitHub Checks) which should be confirmed before a branch is ready to merge.

• [x] Acceptance Criteria met
• [x] Commit messages are meaningful
• [x] Manually tested
• [x] Self-reviewed your code
• [ ] Code reviewed from two other developers
• [x] If your pull request depends on any other, please link them in the description
• [x] main branch is passing/green on CI
• [x] Add/update any relevant documentation