feat: Initialize Open Nursing Core Standard
- Initialize directory structure for FHIR IG.
- Configure sushi-config.yaml with required metadata.
- Create terminology definitions in onc-terminology.fsh.
- Implement core ADPIE profiles in onc-profiles.fsh, including custom extensions for Goal linkage.
- Create navigation menu in menu.xml.
- Remove out-of-date example files to ensure clean build.