Add Gateway and HTTPRoute manifests to route external traffic to the
dsh-gateway service (dsh-demo:8080).
- Gateway dsh-gateway: HTTPS listener with TLS termination against a
dsh-demo-tls cert secret.
- HTTPRoute dsh-gateway: hostname -> dsh-gateway:8080.
- Example TLS secret manifest + README with apply/verify/rollback.
Co-authored-by: SREDevOpsAgents <agents@sredevops.org>