Fix PG monitoring errors

[bpkroth]

Noticed these in some of the CI runs. Might have been there earlier and I missed it. Should probably have a check for that as well as improved checking of results actually being logged.

@anjagruenheid do you mind taking a quick look?

Error:  2024-06-03 20:55:40,800 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor extractQueryMetrics - ERROR: relation "pg_stat_statements" does not exist
  Position: 223
[INFO ] 2024-06-03 20:55:41,719 [main]  com.oltpbenchmark.ThreadBench runRateLimitedMultiPhase - TERMINATE :: Waiting for all terminals to finish ..
Error:  2024-06-03 20:55:41,720 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor extractQueryMetrics - Error when extracting per query metrics.
Error:  2024-06-03 20:55:41,720 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor extractQueryMetrics - ERROR: relation "pg_stat_statements" does not exist
  Position: 223
Error:  2024-06-03 20:55:41,721 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor cleanupCache - Error when cleaning up cached plans.
Error:  2024-06-03 20:55:41,721 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor cleanupCache - ERROR: function pg_stat_statements_reset() does not exist
  Hint: No function matches the given name and argument types. You might need to add explicit type casts.
  Position: 8
[WARN ] 2024-06-03 20:55:41,721 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor writeSingleQueryEventsToCSV - No query events have been recorded, file not written.
[WARN ] 2024-06-03 20:55:41,721 [Thread-5]  com.oltpbenchmark.api.collectors.monitoring.DatabaseMonitor writeRepeatedQueryEventsToCSV - No repeated query events have been recorded, file not written.