fix: remove red herring warp logs on default log-level

The logs added on e95e815483 are red
herrings under normal operation.

This moves them to `log-level=debug` and removes "error" from the
message prefix.

Fixes https://github.com/PostgREST/postgrest/issues/4799

src/PostgREST/Logger.hs

@@ -116,6 +116,9 @@ observationLogger loggerState logLevel obs = case obs of
   o@(JwtCacheLookup _) ->
     when (logLevel >= LogDebug) $ do
       logWithZTime loggerState $ observationMessage o
+  o@(WarpServerObs _) ->
+    when (logLevel >= LogDebug) $ do
+      logWithZTime loggerState $ observationMessage o
   o ->
     logWithZTime loggerState $ observationMessage o