fix: schema cache retrying without backoff

Fixes https://github.com/PostgREST/postgrest/issues/3523.

Now if there's a failure when obtaining the pg version OR schema cache,
we do the same retrying process. This way we don't add two retries.

Refactors and renames the "connectionWorker" to "schemaCacheLoader".
This makes more sense since what we really want is the schema cache,
the version is the pre-requisite for ensuring our
schema cache queries work.

Additionally, we no longer log ` Attempting to connect to the database...`
at startup unnecessarily. This is only logged whenever there's a retry attempt.

src/PostgREST/App.hs

@@ -68,14 +68,14 @@ run appState = do
 
   observer $ AppStartObs prettyVersion
 
-  AppState.connectionWorker appState
-  Unix.installSignalHandlers (AppState.getMainThreadId appState) (AppState.connectionWorker appState) (AppState.reReadConfig False appState)
+  AppState.schemaCacheLoader appState -- Loads the initial SchemaCache
+  Unix.installSignalHandlers (AppState.getMainThreadId appState) (AppState.schemaCacheLoader appState) (AppState.readInDbConfig False appState)
 
   Listener.runListener appState
 
   Admin.runAdmin appState (serverSettings conf)
 
-  let app = postgrest configLogLevel appState (AppState.connectionWorker appState)
+  let app = postgrest configLogLevel appState (AppState.schemaCacheLoader appState)
 
   case configServerUnixSocket of
     Just path -> do