Add statistics to count frequency of saving validity window in the data store

Depending upon the prevailing conditions, reconciliation might choose to store some of the transaction IDs and timestamps along with a K/V pair in the data store. It will be helpful to know how frequently this happens.

These statistics could be:

• Number of pages reconciled with timestamps.
• Number of pages reconciled with transaction IDs
• Number of pages reconciled with the prepared related metadata

Investigate what other statistics we could add. Also since the generation of the reconciliation image happens in a layer separate to putting the image into pages, it might be hard to compute the number of pages for these statistics. If that is the case, what could these statistics track instead of the pages ?