[BUG] Readiness Probe always expects HTTPS

[renaudhager]

What is the bug?

The operator allows disabling port 9200 to listen on HTTP only. However, the readiness probe expects this port to be HTTPS.

How can one reproduce the bug?

Configure the following in your cluster definition:

apiVersion: opensearch.opster.io/v1
kind: OpenSearchCluster
metadata:
  name: my-cluster
  namespace: opensearch
spec:
  general:
    additionalConfig:
      plugins.security.ssl.http.enabled: "false"
...

What is the expected behavior?

The readiness probe should handle this case.

What is your host/environment?

Kubernetes Version: 1.31
OpenSearch Kubernetes Operator Version: 2.7.0
Cloud Provider or Platform: EKS

Do you have any screenshots?

Do you have any additional context?

This would very useful since the current state of the operator prevent it to be use with service mesh and this PR is setting idle for almost a year.