fix: inaccurate Server-Timing durations

The transaction duration was notably off, doing:

```
curl localhost:3000/rpc/sleep?seconds=5 -i
```

Shows `46.1` for the `transaction;dur`, with this fix we obtain
`5007.3`.

Fixes https://github.com/PostgREST/postgrest/issues/4522

This also fixes inaccurate "schema cache queried" logs,
see https://github.com/PostgREST/postgrest/issues/4551.

(cherry picked from commit 013f078bc4)

src/PostgREST/App.hs

@@ -51,13 +51,13 @@ import PostgREST.Observation          (Observation (..))
 import PostgREST.Response.Performance (ServerTiming (..),
                                        serverTimingHeader)
 import PostgREST.SchemaCache          (SchemaCache (..))
+import PostgREST.TimeIt               (timeItT)
 import PostgREST.Version              (docsVersion, prettyVersion)
 
 import qualified Data.ByteString.Char8 as BS
 import qualified Data.List             as L
 import qualified Network.HTTP.Types    as HTTP
 import           Protolude             hiding (Handler)
-import           System.TimeIt         (timeItT)
 
 type Handler = ExceptT Error