Add old readiness probe related ENVs

[kvalliyurnatt]

We are seeing issues with upgrading to 2.14.0 when there are overrides present for the readiness probe, adding the ENVs that have the credentials for the old readiness probe to run successfully should fix that issues
fixes: #8006

[naemono]

Tested with the following manifest successfully

apiVersion: elasticsearch.k8s.elastic.co/v1
kind: Elasticsearch
metadata:
  name: elasticsearch-sample
spec:
  version: 8.15.0
  nodeSets:
  - name: master
    config:
      node.roles: ["master"]
      node.store.allow_mmap: false
    podTemplate:
      metadata:
        labels:
          foo: bar
      spec:
        containers:
        - name: elasticsearch
          readinessProbe:
            exec:
              command:
                - bash
                - -c
                - /mnt/elastic-internal/scripts/readiness-probe-script.sh
            failureThreshold: 3
            initialDelaySeconds: 10
            periodSeconds: 12
            successThreshold: 1
            timeoutSeconds: 12
          resources:
            limits:
              memory: 2Gi
              cpu: 1
    count: 3
  - name: data
    config:
      node.roles: ["data", "ingest", "ml"]
      node.store.allow_mmap: false
    podTemplate:
      metadata:
        labels:
          foo: bar
      spec:
        containers:
        - name: elasticsearch
          readinessProbe:
            exec:
              command:
                - bash
                - -c
                - /mnt/elastic-internal/scripts/readiness-probe-script.sh
            failureThreshold: 3
            initialDelaySeconds: 10
            periodSeconds: 12
            successThreshold: 1
            timeoutSeconds: 12
          resources:
            limits:
              memory: 2Gi
              cpu: 1
          env:
          - name: ES_JAVA_OPTS
            value: "-Xms1g -Xmx1g"
    count: 3

I see the proper env vars set on the sts:

            - name: PROBE_PASSWORD_PATH
              value: /mnt/elastic-internal/pod-mounted-users/elastic-internal-probe
            - name: PROBE_USERNAME
              value: elastic-internal-probe
            - name: READINESS_PROBE_PROTOCOL
              value: https

[naemono]

LGTM as a straight-forward fix

[pebrc]

@ibalat can you open a thread in https://discuss.elastic.co/c/orchestration/eck/79 and we can discuss there. Let's reserve this PR for the discussion of the actual PR

[kvalliyurnatt]

Closing this, as we don't want to reintroduce these ENVs again, we have updated the documentation on the new readiness probe

[kvalliyurnatt]

💚 All backports created successfully

Status	Branch	Result
✅	2.15

Questions ?

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