Add error response examples to API YAML

[benhepworth]

Summary

All error responses in code/API_definitions/session-insights.yaml are missing the examples section inside content.application/json. This is required for Commonalities alignment.

Changes Required

For every error response definition, add an examples section within content.application/json, following the pattern established in CAMARA_common.yaml.

Reference Pattern

See CAMARA_common.yaml line 236 and after:
https://github.com/camaraproject/Commonalities/blob/r3.2/artifacts/CAMARA_common.yaml

References

• Raised during review of PR r1.1 M3 release #55