[Case Modeler] Expose editor as an experimental feature on the workbench

We're actually integrating the new Case Management Editor into the workbench, so at this point, as we already do for the BPMN domain, we'll end up with 2 editors for CM: the legacy (old) one and the new one (Stunner based)

The thing is we want to expose the new CM editor as an experimental feature on the workbench, The main goal is to expose the feature by default only the community side, keeping it as optional on the product side. This way is we can move forward on the code and also get feedback as soon as possible, once we decide it's ready for a release we'll remove it from the "experimental" bag.