feat: postman testing

[lukaskett]

Summary

• Add Postman collection and dev+prod environments that enable testing using:

newman run apps/server/postman/collection.json \
 -e apps/server/postman/environments/dev.json \
 --working-dir apps/server/postman

Checklist

• I linked the related issue or explained why none is needed.
• I ran the relevant checks for this change.
• I updated documentation or changelog entries when needed.
• By submitting this pull request, I agree to the terms in CLA.md in the
  repository root.