Require ReferenceGrant for cross-namepsace access to a Secret by KongPluginInstallation

[programmer04]

Problem Statement

In the current implementation, KongPluginInstallation can reference Secret from any namespace without explicitly granting permission. It imposes security risks and does not align with what K8s recommends.

Proposed Solution

Implement a similar mechanism with the required ReferenceGrant to reference Secrets from other namespaces as implemented for TLS in Gateway. Any required changes/adjustments of the KongPluginInstallation CRD are justifiable.

Acceptance Criteria

• a ReferenceGrant is required for referencing Secret from another namespace than KongPluginInstallation