Type safety - Incremental step 2

[Tcharl]

More type safety on JDL

Related with https://github.com/jhipster/generator-jhipster/issues/26114

Please make sure the below checklist is followed for Pull Requests.

• [x] All continuous integration tests are green
• [x] Tests are added where necessary
• [x] The JDL part is updated if necessary
• [x] jhipster-online is updated if necessary
• [x] Documentation is added/updated where necessary
• [x] Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

When you are still working on the PR, consider converting it to Draft (below reviewers) and adding skip-ci label, you can still see CI build result at your branch.