Add Istio API group to kubeclient

What does this MR do?

Add Istio API group to kubeclient and delegate create_gateway, get_gateway, update_gateway to istio_client.

This MR is in support of #33559 (closed) and will need to be merged in order to allow us to configure the knative-ingress-gateway to enable/disable mTLS.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.