Enable strict modus for domainType

[PaulVanSchayck]

There is a bug/problem with FastAPI, where it doesn't use model_validate_json() when passing model data as POST data. This causes domainType not to be validated in strict mode, when it is passed as str in a JSON.

For now we applied the following workaround:

    @field_validator('domainType', mode='before')
    @classmethod
    def value_to_enum(cls, v):
        if isinstance(v, str):
            return DomainType(v)
        return v

See also: fastapi/fastapi#9868