feat StayExport - Initial Implementation

- Created models for DB and DTOs: StayExportFile
- Added required db migrations.
- Added StayExportService and StayExportServiceFactory for stay exporting services.
- Added configuration options required for StayExport.

src/Somnia.GuestLog/Models/Configuration/StayExportConfig.cs

@@ -0,0 +1,10 @@
+namespace Somnia.GuestLog.Models.Configuration;
+
+public class StayExportConfig
+{
+    public const string SectionName = "StayExport";
+
+    public bool EnableStayExport { get; set; } = false;
+    public string? ExportStorageConnectionString { get; set; }
+    public bool UseSubdirectoryByFormat { get; set; }
+}