Summary:
The class DocDBStatistics was added by commit 52a7dca98e9ace4f2d4e7a299b4bbd6d7528bbbf/D22325.
And pointer to the instance of this class is passed down to IntentAwareIterator.
But we already have struct ReadOperationData to pass current read related data there.

This diff cleans up passing statistics to `IntentAwareIterator` by adding field to `ReadOperationData`.
Jira: DB-12341

Test Plan: Jenkins

Reviewers: esheng, arybochkin

Reviewed By: arybochkin

Subscribers: yql, ybase

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D37118