[Meta] Migrate opensearch-aws-sigv4 gem to this repo

[nhtruong]

Migrate the content of https://github.com/opensearch-project/opensearch-ruby/tree/main/opensearch-aws-sigv4 to this repo

• https://github.com/opensearch-project/opensearch-ruby-aws-sigv4/issues/4
• https://github.com/opensearch-project/opensearch-ruby-aws-sigv4/issues/5
• https://github.com/opensearch-project/opensearch-ruby-aws-sigv4/issues/6
• https://github.com/opensearch-project/opensearch-ruby-aws-sigv4/issues/7
• https://github.com/opensearch-project/opensearch-ruby-aws-sigv4/issues/8

[nhtruong]

All tasks Completed