feat: Add resolved host to "Listening on ..." messages (#3560)

This adds resolved host's IP to "Listening on ..." messages emitted when
app and admin servers start.

src/PostgREST/Network.hs

@@ -0,0 +1,17 @@
+module PostgREST.Network
+  ( resolveHost
+  ) where
+
+import           Data.IP        (fromHostAddress, fromHostAddress6)
+import           Data.String    (IsString (..))
+import qualified Network.Socket as NS
+
+import Protolude
+
+resolveHost :: NS.Socket -> IO (Maybe Text)
+resolveHost sock = do
+  sn <- NS.getSocketName sock
+  case sn of
+    NS.SockAddrInet _ hostAddr ->  pure $ Just $ fromString $ show $ fromHostAddress hostAddr
+    NS.SockAddrInet6 _ _ hostAddr6 _ -> pure $ Just $ fromString $ show $ fromHostAddress6 hostAddr6
+    _ -> pure Nothing