[FEATURE_REQUEST] Lint Kubernetes Gateway API resources

[stehessel]

Description of the problem/feature request
The Kubernetes Gateway API is a successor to the Kubernetes Ingress API. It recently graduated to beta. Many big K8s projects are adding support for Gateway API - e.g. Istio intends to make it the default for future API traffic management. In other words, it looks like Gateway API will eventually replace many of the existing custom Ingress solutions. It would therefore be nice to follow suit and support linting of Gateway resources in kube-linter.

Additional context
Some rules that could make sense (no claim of completeness):

• TLS secret reference in listeners is valid.
• Listener names are unique within a Gateway.
• The GatewayClass reference of a Gateway is valid.
• GatewayTLSConfig is defined iff protocol is HTTPS or TLS.
• allowedRoutes binds to at least one route.
• backendRefs in routes are valid.