Delivery-service tenancy based access control - Steering Target

We have recently added "tenancy" to the project.
With tenancy, every resource have a tenant, where resource can be a delivery-service, a server (future) and even a user.
We are now starting to enforce access-control based on the resource tenancy. A user can manage a resource only if the resource is under the user tenancy.

This JIRA deals with another step of "delivery-service as a resource" - enforcing via the API access control on DS steering target: In order to add a steering target DS1 to steering DS ST1, the user should have access to the tenants of DS1 and ST1. In order to read the record, access to ST1 is enough