[v3.*] set default replicas for system indexes

[sbruzzese902]

Hi 👋

With @Deepzima and @ettoreciarcia we discovered that by default all system indexes in OpenSearch (in the form .opendistro*) have by default the replicas set at 1.

This causes all our single-node OpenSearch deploy to be in the yellow state.

We fixed the issue using the following strategy:

• deleted the unassigned shards ( in our case they were .opendistro-ism-config and .opendistro-job-scheduler-lock
• apply the following patch as suggested here and after that launch manually the ism-policy job

curl -H 'Content-Type: application/json' -X PUT \
    -d '{
  "priority": 0,
  "index_patterns": [
    ".*"
  ],
  "template": {
  "settings": {
    "index": {
      "auto_expand_replicas": "0-1"
    }
  }
  }
}' \
  http://<opensearch_url>/_index_template/auto_expand_replicas

Probably this should be set together with our index patterns using the cronjob or - better - from the OpenSearch configuration file, if possible.