Allow `PluginBindings` to be used on Kubernetes CRDs for Gateway Configuration

[mlavacca]

Problem Statement

#1 introduced the new KongPluginBinding CRD to allow users to bind plugins to specific kong resources.

We need to add KongPluginBinding support for regular Kubernetes resources to be configured on Kong Gateway as well.

Proposed Solution

We could add a new genericEntityRef (name to be defined) field in the KongPluginBinding to allow users to bind plugins on Kubernetes Services, ingresses, HTTPRoutes, etc. as well.

Additional Information

Acceptance Criteria

• As a user, I can use the KongPluginBinding resource to configure plugins in a Kong Gateway.

[mlavacca]

Closing as superseded by #11