feat: notifications

[Rizzy-2005]

• Added the basic event submission notification for both the host and the associated faculty to approve it.
• Added the workflow-step notification, which mainly includes the notification sent to organizers to let them know about each stage and also sent to approvers.
• Added the notification to let the organizers know whether the entire event is approved or denied at some stage.
• Adding the rest of the necessary notification features in the coming days, most probably using bullMQ.