Add Index Stats API (#4892)

* Add Index Stats API

Signed-off-by: Fanit Kolchina <[email protected]>

* Reword for clarity

Signed-off-by: Fanit Kolchina <[email protected]>

* Apply suggestions from code review

Co-authored-by: Nathan Bower <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>

* Update _api-reference/index-apis/stats.md

Signed-off-by: kolchfa-aws <[email protected]>

* Implemented editorial comments

Signed-off-by: Fanit Kolchina <[email protected]>

* Implement editorial comments

Signed-off-by: Fanit Kolchina <[email protected]>

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Signed-off-by: Fanit Kolchina <[email protected]>
Signed-off-by: kolchfa-aws <[email protected]>
Co-authored-by: Nathan Bower <[email protected]>
(cherry picked from commit 871f8ab)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>