refactor: move socket creation and management to App module

Right now listening sockets initialization, management and usage is split between App, AppState and Admin modules: they are created in AppState.init and remembered in AppState but used only in App and Admin.

It has several negative consequences:
- sockets are initialized even if not needed (eg. command line invocations like dump-config or dump-schema)
- it is impossible to start listening on a socket after initial schema cache load because it requires AppState

This change decouples listen socket management from AppState. Sockets are created only when needed (ie. not in command line tools invocation) and passed to admin application and to Warp by the App module.

test/spec/Main.hs

@@ -84,13 +84,12 @@ main = do
 
   -- cached schema cache so most tests run fast
   baseSchemaCache <- loadSCache pool testCfg
-  sockets <- AppState.initSockets testCfg
   loggerState <- Logger.init
   metricsState <- Metrics.init (configDbPoolSize testCfg)
 
   let
     initApp sCache st config = do
-      appState <- AppState.initWithPool sockets pool config loggerState metricsState (Metrics.observationMetrics metricsState)
+      appState <- AppState.initWithPool pool config loggerState metricsState (Metrics.observationMetrics metricsState)
       AppState.putPgVersion appState actualPgVersion
       AppState.putSchemaCache appState (Just sCache)
       return (st, postgrest (configLogLevel config) appState (pure ()))