feat: log pool maximum size

It's important for observability to have an historic trace of the pool
size. Currently we expose it on the metrics endpoint, but not all
deployments use it.

This logs the pool size after the successful connection log to make it
more visible:

<timestamp>: Connection Pool initialized with a maximum size of 4 connections

src/PostgREST/App.hs

@@ -67,8 +67,6 @@ run appState = do
   let observer = AppState.getObserver appState
   conf@AppConfig{..} <- AppState.getConfig appState
 
-  observer $ AppStartObs prettyVersion
-
   AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
   Unix.installSignalHandlers (AppState.getMainThreadId appState) (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)