[FEATURE] make OpenSearchISMPolicy support email channel notification

[latituder]

Is your feature request related to a problem?

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I use opensearch Operator deploy my openserach-cluster.
the opensearch Operator also brings a CRD “OpenSearchISMPolicy”, which helps to use a yaml to deinfe ISM.

In the Opensearch UI, if I manually setup an ISM policy, then I can choose a configured notification channel (email), and write an email template.

hoewver, in CR OpenSearchISMPolicy, I see the notifcation doesn’t has email option.

$ kc explain OpenSearchISMPolicy.spec.errorNotification.destination
GROUP:      opensearch.opster.io
KIND:       OpenSearchISMPolicy
VERSION:    v1

FIELD: destination <Object>


DESCRIPTION:
    The destination URL.
    
FIELDS:
  amazon        <Object>
    <no description>

  chime <Object>
    <no description>

  customWebhook <Object>
    <no description>

  slack <Object>
    <no description>

What solution would you like?

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Ideally, I’d like to set the OpenSearchISMPolicy like this:

apiVersion: opensearch.opster.io/v1
kind: OpenSearchISMPolicy
metadata:
  name: logs-rollover-retention
spec:
  opensearchCluster:
    name: app-logging-opensearch
  description: "set index rollover then wait and retension"
  policyId: logs-rollover-retention
  defaultState: young_indexes
  ismTemplate:
    indexPatterns:
       - logs-*
    priority:  1
  errorNotification:
    channel: my-email-channel # this email channel already configured and tested
    destination: 
        <may I refer an email receiver group name here?>
    messageTemplate:
      source: "APP logging OpenSearch ISM job: The index {{ctx.index}} failed during ISM policy execution"
  states:
    - name: young_indexes
      actions:
.......

apiVersion: opensearch.opster.io/v1
kind: OpenSearchISMPolicy
metadata:
name: logs-rollover-retention
spec:
opensearchCluster:

What alternatives have you considered?

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[prudhvigodithi]

[Triage]
Thanks @latituder. OpenSearchISMPolicy is for index management, we should have a new CRD for alerting and notifications ?
https://opensearch.org/docs/latest/observing-your-data/notifications/index/
Adding @gaiksaya @swoehrl-mw