Provide a longer data retention period for Session details and statistics

It's difficult to identify idle sessions/connections that are problematic causing downstream issues such as contention over time - this is especially difficult when not all the information is available when retroactively troubleshooting an issue in the past.

We should capture and persist Sessions details (e.g., which transaction and statements were execution) and statistics (idle vs active vs blocked) over time to allow correlation with other signals such as metrics or SQL activity.

Jira issue: CRDB-35955

The issue names no files, tests, or entry points. Start by locating the existing session details and statistics collection and retention paths, then determine the persisted data and retention behavior needed for historical correlation; done means session state and relevant transaction or statement details remain available for the requested longer period.

Written by the indexing model from the issue text.