refactor(Program): simplify Quartz job registration and add EnvelopeTaskApiJob

- Replaced manual FinishEnvelopeJob Quartz setup with ScheduleJobDefault extension
- Added scheduling for EnvelopeTaskApiJob
- Updated using directives to include EnvelopeGenerator.Finalizer namespace
- Improved maintainability by removing redundant Quartz configuration logic

EnvelopeGenerator.Finalizer/appsettings.Job.json

@@ -1,5 +1,8 @@
 {
   "FinishEnvelopeJob": {
     "CronExpression": "* * * * * ?"
+  },
+  "EnvelopeTaskApiJob": {
+    "CronExpression": "* * * * * ?"
   }
 }