[Examples Fix] Fixed examples provided against few resources

[premkirank]

Description

• tested these examples against the latest opensearch terraform provider i.e. 2.1.0 (https://registry.terraform.io/providers/opensearch-project/opensearch/latest/docs)
• fixes examples listed against resources opensearch_index and opensearch_index_template

Issues Resolved

• Fixes #111

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[prudhvigodithi]

Thanks @premkirank.