In the response payload of the `GET /trackers/id` REST route, the title key in the semantic part is missing when the title semantic is undefined for the target tracker.

In the types defined in @tuleap/plugin-tracker-rest-api-type for TS apps, the title key of the SemanticRepresentation is marked "always there" while this is not the case. It should be mark as potentially missing, so developer are forced to be more careful it exists before trying to get the field id associated to the title semantic.