refactor(config): allow GdPicture license key from configuration

- Updated GdPictureOptions setup to read license key from `GdPictureLicenseKey` config value.
- Falls back to reading from third-party module if config key is not set.

EnvelopeGenerator.Finalizer/Program.cs

@@ -92,8 +92,9 @@ try
             var licenseKey = "GDPICTURE";
             using var scope = sp.CreateScope();
             var mediator = scope.ServiceProvider.GetRequiredService<IMediator>();
-            opt.License = mediator.ReadThirdPartyModuleLicenseAsync(licenseKey).GetAwaiter().GetResult()
-            ?? throw new InvalidOperationException($"License record not found for key: {licenseKey}");
+            opt.License = config["GdPictureLicenseKey"] 
+                ?? mediator.ReadThirdPartyModuleLicenseAsync(licenseKey).GetAwaiter().GetResult()
+                ?? throw new InvalidOperationException($"License record not found for key: {licenseKey}");
         });
 
     var host = builder.Build();