Support adding of gRPC Routes for Kubernetes Gateway Api Resource

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Is your feature request related to a problem? Please describe the problem.

I would like to create not only http Routes. My current problem is that I have an Zitadel instance as IdP and I want to talk to its management api via gRPC.

### Describe the solution you'd like

Imagine I have some AppHost Programm.cs code like:
```
var testGateway = k8s.AddGateway("test-gateway")
.WithGatewayClass(gatewayClass)
.WithHostname("*.test.me")
...
.WithTls();

var zitadel = ... // Could be any other backend inside the cluster

testGateway.WithRoute("auth.test.me", "/", zitadel, kind: GatewayRouteKind.GRPC); // default could stay as GatewayRouteKind.HTTP
```

would then create a yaml like:
```
apiVersion: gateway.networking.k8s.io/v1
kind: GRPCRoute
metadata:
name: {referenceName}-grpc-route
namespace: {namespace}
spec:
parentRefs:
- name: {gatewayName}
sectionName: https
hostnames:
- auth.test.me
rules:
- backendRefs:
- name: {referenceName}
port: 8080
```

### Additional context

_No response_

Start from the AppHost Program.cs example using AddGateway, WithGatewayClass, WithHostname, WithTls, and WithRoute. Trace how GatewayRouteKind.HTTP is handled and compare the requested GRPCRoute YAML; done means a gRPC route can be configured and produces the shown Gateway API resource.

Written by the indexing model from the issue text.