Allow study subsystem to retrieve input elements for participant attributes

[Whathecode]

Expected participant data is communicated to the client on study deployment (PrimaryDeviceDeployment), but from the studies subsystem is only accessible by accessing the study protocol.

I just noticed that although you do receive expected input elements on PrimaryDeviceDeployment through the expectedParticipantData property, this doesn't help a web interface as part of study management to display these elements.

When you receive known types and you have access to the CARP runtime, you can retrieve the statically defined input types. But, for custom types, you'd need access to the original protocol to discern the input elements (or derived types through which input elements are passed, such as PrimaryDeviceDeployment). This is undesirable coupling.

Incorporating support for retrieving InputElement's as part of ParticipationService will make sense. Maybe they can optionally be requested as part of getParticipantData. Or, a new endpoint to retrieve input elements could be added. I'll give this some thought. Both seem backwards compatible.

An added benefit may be this also allows the studies subsystem to run on an older version of CARP than the deployments subsystem, at least for this dependency. The study manager could choose not to rely on carp.common to retrieve InputElement's, and instead retrieve them from the deployments subsystem.