core (types): Renamed `libervia.backend.core.core_types.MessageData` to `MessageDataLegacy`: There are 2 concurrent models, this one is an historical legacy. The type to use the one from `libervia.backend.models.core`, and it will progressively be used everywhere and fully based on Pydantic.

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)