opensearch_data_stream: Check if the index template exists every time before pushing data

[adiforluls]

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Steps to replicate

I am running OpenSearch and Fluentd with ephemeral storage in a Kubernetes environment. Sometimes OpenSearch pod can restart, and with ephemeral storage the index template created by Fluentd goes away once OpenSearch instance comes back up, and now the data is instead written to an index with same name as data_stream_name. The problem is because we maintain a local cache and decide if we need to create index template instead of checking the OpenSearch host.

Provide example config and message

Expected Behavior or What you need to ask

Even if index template is somehow deleted in OpenSearch, it should be recreated by fluent-plugin-opensearch

...

Using Fluentd and OpenSearch plugin versions

OpenSearch v2.3.0
Fluentd v1.14.5

• OS version
• Bare Metal or within Docker or Kubernetes or others?
• Fluentd v1.0 or later
  • paste result of fluentd --version or td-agent --version
• OpenSearch plugin version
  • paste boot log of fluentd or td-agent
  • paste result of fluent-gem list, td-agent-gem list or your Gemfile.lock
• OpenSearch version (optional)
• OpenSearch template(s) (optional)