missing doc to create a secret for gateway api HTTPS protocol

## Expected Behavior
Doc should explain how to create the TLS secret for gateway API HTTPS protocol

it should be working with [this doc](https://kserve.github.io/website/master/admin/gatewayapi_migration/#8-verify-the-gateway-api-configuration)
```
kubectl get svc kserve-ingress-gateway -l serving.kserve.io/gateway=kserve-ingress-gateway -A
```
but it showed nothing because the gateway is not adding the label properly because the secret does not exist

~~~
- attachedRoutes: 2
conditions:
- lastTransitionTime: "2025-03-17T20:34:30Z"
message: Secret kserve/my-secret does not exist.
observedGeneration: 1
reason: InvalidCertificateRef
status: "False"
type: ResolvedRefs
- lastTransitionTime: "2025-03-17T20:34:30Z"
message: Listener is invalid, see other Conditions for details.
observedGeneration: 1
reason: Invalid
status: "False"
type: Programmed
name: https
supportedKinds:
- group: gateway.networking.k8s.io
kind: HTTPRoute
- group: gateway.networking.k8s.io
kind: GRPCRoute
~~~

## Actual Behavior
it does not show the way to generate tls so it is not possible to create a gateway properly.

## Steps to Reproduce the Problem

1.When it tries to access https, it will fail

## Additional Info
**Additional context**
Add any other context about the problem here.

**Install information:**
- Platform (GKE, IKS, AKS, OnPrem, etc.):
- KServe Version:

Start with the Gateway API migration documentation linked in the issue, especially the “Verify the Gateway API configuration” section, and review the shown kubectl command and Gateway status. Document how to create the TLS secret required by the HTTPS listener. Done when a reader can create the secret and verify a properly configured gateway using the documented steps.

Written by the indexing model from the issue text.