fix(task-manager): refactored email mutation

This MR is to fix the issue encountered on biophysics colab instance, where the task manager notifications are being sent, while their status is not being received on the front end. The email mutation used for sending notifications was supposed to return a response variable. There had been enhancements to include invitation object replacing the response variable, but we don't need invitation object at all places. I have created this MR as a fix for notifications to work at all the places.