Add Automation for ReferenceGrant Creation with Gateway API and HTTPRoute

This PR is a feature to automatically create ReferenceGrant resources when using Flagger with Gateway API and HTTPRoute. It addresses scenarios where an HTTPRoute needs to route traffic to a Service in a different namespace, which requires a ReferenceGrant to function correctly.

Issue Reference

This PR resolves fluxcd/flagger#1718.

Implementation Details

• Conditional Automation: The creation of ReferenceGrant is only triggered if an HTTPRoute is configured to route traffic to a Service in a different namespace. If the Service resides in the same namespace as the HTTPRoute, no ReferenceGrant is generated, ensuring minimal and precise resource management.
• Namespace Awareness: The implementation checks the namespace of the target Service and dynamically creates the ReferenceGrant only when necessary, adhering to the Gateway API requirements.