Adding a remind unconfirmed button to availability page

[EdgarButtner]

Changes

Adding button to remind unconfirmed members on the availability page.

Notes

Still need to test using Postman

Test Cases

All tests are in calender.test.ts

• Reminder fails if event does not exist
• Reminder fails if event has been deleted
• Reminder fails if the creator is not the one sending the notification
• Reminder succeeds and sends
• Reminder succeeds when people have all confirmed
• ...

Screenshots

Normal size:

Smallest Screen: (Might want to rework availability page as a whole on mobile as it is a bit unwieldy)

To Do

• Test using Postmon
• Make sure all code is correct and no bugs

Checklist

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Closes #4203