`ReferenceGrant` cannot be disabled

[mlavacca]

Problem Statement

In the HybridGateway controllers, we currently have a check on the existence of the ReferenceGrant CRD to enable cross-namespace protection. This means that such a mechanism protection can be disabled.
Since ReferenceGrant is a graduated API and belongs to the standard channel, it cannot be disabled by the user.

Acceptance Criteria

• In the HybridGateway controller, the ReferenceGrant checks are always enforced