Deprecate GSLB CRD

[ytsarev]

The proposal is to deprecate core GSLB CRD and rely purely on standard Ingress annotations.

Motivation:

• Currently we already have Ingress -> Gslb creation logic here https://www.k8gb.io/docs/ingress_annotations.html
• It already led to the issues around associated reconciliation, annotation propagation and keeping Ingress and Gslb in sync.
• It is not clear what should be source of truth - Gslb or Ingress
• Gslb is just embedding/wrapping Ingress type within itself so relying purely on Ingress+Annotations should not lead to dramatic changes within the k8gb controller logic

[ytsarev]

After some discussions with the maintainers team:

• We can actually keep Gslb CRD but make it read-only status exposing resource to keep contextual GSLB information that does not fit into the standard Ingress event stream
• We need to come up with reliable migration plan to not to break stuff for existing k8gb users

[ytsarev]

We agreed to keep Gslb CRD and enable flexible referencing of various networking resources instead of full switch to Ingress.
First case of resource reference implemented in #1557