Add inheritance to generated JSON schema

[tonysviews]

Is your feature request related to a problem? Please describe.
When validating data using the JSON schema generated when a CET is created/updated, the validation is incomplete when the entity inherits some of its properties from a parent entity.

Describe the solution you'd like
The generated JSON schema should reflect the inheritance of properties between child and parent entities.

Describe alternatives you've considered
The JSON Schema standard does not define inheritance Explain why inheritance isn't the right model

However, it is possible to validate a schema using the allOf property, which could be enough for our purposes of doing validation of data from the frontend: How to do inheritance?

Additional context
N/A

[ClementBareth]

@tonysviews I let you test