Fix fleet alert acknowledgements path to use ProgramData/ShopDB

Changed FleetAlertStore to save acknowledgements in:
  ProgramData/ShopDB/FleetAlerts/acknowledged-alerts.json

Instead of:
  ProgramData/ShopDbAgent/acknowledged-alerts.json

Now matches the standard folder structure used by other agent components.

agent/ShopDbEndpointAgent.Core/FleetAlertStore.cs

@@ -10,7 +10,8 @@ public sealed class FleetAlertStore
 {
     private static readonly string DataDir = Path.Combine(
         Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData),
-        "ShopDbAgent");
+        "ShopDB",
+        "FleetAlerts");
 
     private static readonly string StoreFile = Path.Combine(DataDir, "acknowledged-alerts.json");