add validation: cell suspensions linked to files

**Describe the issue**

- Test name: cell suspensions linked to files
- Test Description: Check that every cell suspension is linked to an analysis file or sequence file
- Cypher query:
```
MATCH (c:cell_suspension)
WHERE NOT (c)-[]-(:sequence_file) OR (c)-[]-(:analysis_file)
RETURN c, "This cell suspension is not linked to any file", labels(c)
```

**Acceptance criteria**

- [ ] The test has been reviewed
- [ ] The test has been implemented into the `graph_test_set` folder