[FLINK-38047] Bump cert-manager from v1.8.2 to v1.18.2 (#992)

* [FLINK-38047] Bump cert-manager from v1.8.2 to v1.18.2

This PR updates the cert-manager version used in the Flink Kubernetes
Operator from v1.8.2 to v1.18.2. The changes include:

- Updated cert-manager in e2e-tests/cert-manager.yaml to v1.18.2 (source: https://github.com/jetstack/cert-manager/releases/download/v1.18.2/cert-manager.yaml)
- Updated documentation references in helm.md and quick-start.md to use
  the new cert-manager version

* [FLINK-38047] Switch `kubectl create` with `kubectl apply`

Author: kumar-mallikarjuna

docs/content.zh/docs/operations/helm.md

@@ -135,7 +135,7 @@ __Notice__: The pod resources should be set as your workload in different enviro
 
 In order to use the webhooks in the operator, you must install the cert-manager on the Kubernetes cluster:
 ```
-kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.8.2/cert-manager.yaml
+kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.18.2/cert-manager.yaml
 ```
 
 The webhooks can be disabled during helm install by passing the `--set webhook.create=false` parameter or editing the `values.yaml` directly.

docs/content.zh/docs/try-flink-kubernetes-operator/quick-start.md

@@ -68,7 +68,7 @@ We also recommend [k9s](https://k9scli.io/) as GUI for kubernetes, but it is opt
 
 Install the certificate manager on your Kubernetes cluster to enable adding the webhook component (only needed once per Kubernetes cluster):
 ```bash
-kubectl create -f https://github.com/jetstack/cert-manager/releases/download/v1.8.2/cert-manager.yaml
+kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.18.2/cert-manager.yaml
 ```
 
 {{< hint info >}}

docs/content/docs/operations/helm.md

@@ -139,7 +139,7 @@ __Notice__: The pod resources should be set as your workload in different enviro
 
 In order to use the webhooks in the operator, you must install the cert-manager on the Kubernetes cluster:
 ```
-kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.8.2/cert-manager.yaml
+kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.18.2/cert-manager.yaml
 ```
 
 The webhooks can be disabled during helm install by passing the `--set webhook.create=false` parameter or editing the `values.yaml` directly.

docs/content/docs/try-flink-kubernetes-operator/quick-start.md

@@ -68,7 +68,7 @@ We also recommend [k9s](https://k9scli.io/) as GUI for kubernetes, but it is opt
 
 Install the certificate manager on your Kubernetes cluster to enable adding the webhook component (only needed once per Kubernetes cluster):
 ```bash
-kubectl create -f https://github.com/jetstack/cert-manager/releases/download/v1.8.2/cert-manager.yaml
+kubectl apply -f https://github.com/jetstack/cert-manager/releases/download/v1.18.2/cert-manager.yaml
 ```
 
 {{< hint info >}}