Add filters, throttling, and connection test

clients/photobooth-uploader/PhotoboothUploader/Services/UploadService.cs

@@ -108,6 +108,10 @@ public sealed class UploadService
                 finally
                 {
                     _pending.TryRemove(path, out _);
+                    if (settings.UploadDelayMs > 0)
+                    {
+                        await Task.Delay(settings.UploadDelayMs, token);
+                    }
                 }
             }
         }