BUG #18046: stats collection behaviour change is affecting the usability of information.

The following bug has been logged on the website:

Bug reference: 18046
Logged by: Jobin Augustine
Email address: jobinau(at)gmail(dot)com
PostgreSQL version: 15.3
Operating system: CentOS/RHEL
Description:

After stats collection changes in PG 15, The behaviour stats_reset
information is changed. which is adversely affecting the usability of data
presented in the view.
```
select stats_reset from pg_stat_database;
```
Before PG15, stats_reset was always populated so that the user knows the
cumulative values presented are of how many days.
But unfortunately, PG 15 keeps it null unless there is an explicit reset
(pg_stat_reset). The value goes again null if there is a reset due to a
crash.
So on a regular system, the User can't understand the cumulative values
presented in the view.