[FEATURE] Support dataStream inside OpensearchIndexTemplate

[cgroschupp]

To allow data streams to be created directly from an index template, it is necessary to support this in the OpensearchIndexTemplate resource.

Example OpensearchIndexTemplate:

apiVersion: opensearch.opster.io/v1
kind: OpensearchIndexTemplate
metadata:
  name: logs
spec:
  opensearchCluster:
    name: test
  name: logs
  indexPatterns:
    - "logs-*"
  dataStream: {}

[salyh]

This would absolutely make sense. Thank you for your contribution.