add data schemas

[simontaurus]

Description

add data schemas for general Entity, Product, Process, ConceptSchema and Concept
see also: sentier-dev/sentier.dev#24 (comment)

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I'm aware of the contributing guidelines.
• I've created logical separate commits and followed the commit message format.
• If this PR resolves or addresses an issue, I've linked it in the commit message.
• I've added relevant test cases.
• I've added relevant documentation.
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please make sure this has been discussed in a github issue.