refactor: move logStdout/corsPolicy to Middleware

* remove configQuiet from Config

configQuiet was not an end user setting.
The logging setup is now an internal parameter.

* move proxy uri validation to Private dir

src/PostgREST/Types.hs

@@ -535,3 +535,6 @@ data ConnectionStatus
   | Connected PgVersion
   | FatalConnectionError Text
   deriving (Eq, Show)
+
+-- | Logging setup
+data LogSetup = LogQuiet | LogStdout deriving (Eq, Show)