Make samples compatible with OpenSearch 2.x.

[dblock]

Signed-off-by: dblock dblock@amazon.com

• Use _doc that works on both 1.x and 2.x versions.
• Create a delete the index. Not really required but good to cleanup.

Closes #91.

Pull Request Checklist:

• [x] I have added a contribution line at the top of CHANGELOG.md.

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