POST /register should normalize properties before saving them

[Syndesi]

The endpoint POST /register currently copies properties directly from the user's request to the database, which might result in unwanted behavior. Instead, the provided properties should first be normalized / validated, similar to the way it is handled in the POST / and POST /<uuid> endpoints. They are currently using the service src/Service/CreateElementFromRawDataService.php.

Tasks:

• Check if other user endpoints are also copying raw properties directly to the database. If those are found, add them to this issue.
• Modify those endpoints to use the CreateElementFromRawDataService or similar services.
• Update unit tests.
• Verify that existing feature tests are working.
• Add a new feature test, where the correct behavior can be tested? Although at this moment, no testable normalization takes place iirc - so the feature test would have to execute a database call against Neo4j directly?