Use KongObjectRef in Konnect entities references

[czeslavo]

Problem Statement

In Konnect entities CRDs we employed different types to express references to other objects. The goal of this issue is to use KongObjectRef where applicable instead of using multiple reference types that have equal schema (required name, optional namespace).

Acceptance Criteria

• If a Konnect entity CRD refers to an object, it uses KongObjectRef as a reference type