refactor: Remove unnecessary SQL.UsageError parameter from PoolAcqTimeoutObs

PoolAcqTimeoutObs is always created with SQL.AcquisitionTimeoutUsageError so the parameter does not provide any useful information.
On the other hand, it complicates debouncing logic in Logger as logWithDebounce has to lazily create the debouncer (which is error prone and hence the logic has a race condition).

This change removes the parameter from PoolAcqTimeoutObs. It is a prerequisite to simplifying logWithDebounce.

src/PostgREST/Metrics.hs

@@ -50,7 +50,7 @@ init configDbPoolSize = do
 -- Only some observations are used as metrics
 observationMetrics :: MetricsState -> ObservationHandler
 observationMetrics MetricsState{..} obs = case obs of
-  (PoolAcqTimeoutObs _) -> do
+  PoolAcqTimeoutObs -> do
     incCounter poolTimeouts
   (HasqlPoolObs (SQL.ConnectionObservation _ status)) -> case status of
      SQL.ReadyForUseConnectionStatus  -> do