Improve the example to demo multi-tenancy for `storeAdmin` roles

[pulkitsinghal]

Write CURL requests to demo and make any code changes needed:

1. Have all 4 store admins create a StuffModel that they own.
2. Demo that 2 store admins from orgA can GET /api/StuffModels and it lists all the stuff across OrgA
3. Demo that store admins from orgA cannot GET any stuff from orgB
4. Demo that 2 store admins from orgB can GET /api/StuffModels and it lists all the stuff across OrgB
5. Demo that store admins from orgB cannot GET any stuff from orgA

[pulkitsinghal]

Found a bug when sanity testing the previous curl requests. Will fix that first.