feat(provider): migrate to dedicated OpenSearch provider

[steveteuber]

This pull request migrates all resources to the new dedicated provider for OpenSearch. Fixes #53.

[steveteuber]

Unfortunately, terraform state mv and moved blocks are not working.
All affected elasticsearch_* resources must be migrated manually after the upgrade...

terraform state pull > elasticsearch-provider.tfstate
jq '.resources[].type |= sub("^elasticsearch_(opensearch_)?"; "opensearch_")' elasticsearch-provider.tfstate > opensearch-provider.tfstate
terraform state replace-provider -state=opensearch-provider.tfstate -auto-approve phillbaker/elasticsearch opensearch-project/opensearch
terraform state push opensearch-provider.tfstate

Additionally, you have to migrate all legacy index templates to the new format. Actually the aliases, mappings, and settings configs are now nested underneath template: https://opensearch.org/docs/latest/im-plugin/index-templates/

[github-actions]

🎉 This PR is included in version 2.0.0 🎉

The release is available on GitHub release

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