Add inventory relations model and API structure

backend/app/main.py

@@ -3,8 +3,10 @@ from fastapi.middleware.cors import CORSMiddleware
 
 from app.routers.discoveries import router as discoveries_router
 from app.routers.health import router as health_router
+from app.routers.inventory import router as inventory_router
 from app.routers.jobs import router as jobs_router
 from app.routers.objects import router as objects_router
+from app.routers.relations import router as relations_router
 
 app = FastAPI(title='NetMapper Backend', version='0.1.0')
 
@@ -20,3 +22,5 @@ app.include_router(health_router)
 app.include_router(objects_router)
 app.include_router(jobs_router)
 app.include_router(discoveries_router)
+app.include_router(inventory_router)
+app.include_router(relations_router)