addVersion method
Add a new version for the specified study protocol, of which a previous
version with the same id, ownerId, and name is already stored.
versionTag is an optional unique label used to identify this specific
version of the protocol. The current date/time by default.
Implementation
@override
Future<void> addVersion(StudyProtocol protocol, [String? versionTag]) async =>
await _rpc(AddVersion(protocol, versionTag));