v2.0.0

Upgrade OpenSearch version to 3.1 @goruha (#220)

## what * Upgrade OpenSearch version to 3.1 in examples * Upgrade ElasticSearch version to 7.10 in examples

why

• OpenSearch 2.9 ended the standard support
• ElasticSearch 7.10 ended the standard support

references

• https://docs.aws.amazon.com/opensearch-service/latest/developerguide/what-is.html#choosing-version