[Maintenance] - Frontend Move Notifications to Event Level

Description

We want users to be able to toggle notifications at the event level. Currently this is controlled at the Event Type level through admin tools.

Remove 'Send Slack Notifications' from Admin Tools event type forms and add a toggle to the Event create and edit forms so users can control Slack notifications per event.

Blocked by the backend changes in #4090

Proposed Solution

• remove checkbox from admin tools EventTypeFormModal and EditEventTypeModal
• add toggle to event create form & event edit form (constrained by the same !teams && !workPackage disable logic that currently lives in the event
  type form)
  • apply same disable logic currently used in the event type form: disable and default to false when neither teams nor work
    packages are selected for the event
• update hooks to remove sendSlackNotifications from Event Type and move to Event paths
• update any types that reference EventType.sendSlackNotifications

Acceptance Criteria

• screenshots of calendar event create/edit modals w/ toggle
• screenshots of admin tools edit event type modal w/o checkbox

Screenshots

Update the notification value to a toggle in the Edit/Create Event modals

---

Remove send slack notifications toggle from admin tools