docs: use kubectl patch with `--type=merge` in docs

[kranurag7]

Description:

I was trying out the following docs here https://gateway.envoyproxy.io/docs/tasks/security/tls-cert-manager/#creating-a-tls-gateway-listener the docs as of now suggests the following command for patch using --patch-file flag. This is not working out for me somehow. (I'm using bash shell)

$ kubectl patch gateway eg --patch-file=- <<EOF
metadata:
  annotations:
    cert-manager.io/cluster-issuer: selfsigned
    cert-manager.io/common-name: "Hello World!"
spec:
  listeners:
  - name: https
    protocol: HTTPS
    hostname: www.example.com
    port: 443
    tls:
      mode: Terminate
      certificateRefs:
      - kind: Secret
        name: eg-https
EOF
error: unable to read patch file: open -: no such file or directory
$ kubectl version
Client Version: v1.30.1
Kustomize Version: v5.0.4-0.20230601165947-6ce0bf390ce3
Server Version: v1.30.2

I updated the command and used the following:

$ kubectl patch gateway eg --patch '
metadata:
  annotations:
    cert-manager.io/cluster-issuer: selfsigned
    cert-manager.io/common-name: "Hello World!"
spec:
  listeners:
  - name: https
    protocol: HTTPS
    hostname: www.example.com
    port: 443
    tls:
      mode: Terminate
      certificateRefs:
      - kind: Secret
        name: eg-https
' --type=merge
gateway.gateway.networking.k8s.io/eg patched

This worked good for me. Is there something I'm missing in the first case which is documented as of now.

[optional Relevant Links:]

slack discussion: https://envoyproxy.slack.com/archives/C03E6NHLESV/p1723037137777729

[arkodg]

he @kranurag7 thanks for surfacing this issue, would be great if you can fix it in the docs

[github-actions[bot]]

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