feat: add draft semantic models for data exchange requests & approvals

[gobica]

Description

• add draft semantic models for data exchange requests & approvals

Related to #1094

Pre-review checks

Please ensure to do as many of the following checks as possible, before asking for committer review:

• DEPENDENCIES are up-to-date. Dash license tool. Committers can open IP issues for restricted libs.
• Copyright and license header are present on all affected files (TRG 7.02
• Documentation Notice are present on all affected files (TRG 7.07)
• If helm chart has been changed, the chart version has been bumped to either next major, minor or patch level (compared to released chart).
• Changelog updated (changelog.md) with PR reference and brief summary.
• Frontend version bumped, if needed (frontend/package.json, frontend/package-lock.json)
• Backend version bumped, if needed (backend/pom.xml)
• Open API specification updated, if controllers have been changed (use python script scripts/generate_openapi_yaml.py with running customer backend)