add query group stats constructs

[kaushalmahi12]

Description

This change introduces constructs to hold live view of query group level stats and point in time view of query group stats. Post these changes we will need changes to hook these constructs with various request events i,e; completions, failures, cancellations and rejections.

Related Issues

Resolves #https://github.com/opensearch-project/OpenSearch/issues/15120 RFC: https://github.com/opensearch-project/OpenSearch/issues/12342

Check List

• [X] Functionality includes testing.
• [ ] API changes companion pull request created, if applicable.
• [ ] Public documentation issue/PR created, if applicable.

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