Implement missing statistics

[dat2]

Is your feature request related to a problem? Please describe.

I noticed that the total_query_time and total_xact_time statistics have no Event and no methods to update it in the Collector.

When working on https://github.com/levkk/pgcat/pull/107 I saw that these statistics were always zero and dug a bit deeper.

Describe the solution you'd like

Non zero metric values :)

Describe alternatives you've considered

Additional context