UnRSVP Warning Modal + Hide Options upon unRSVP

[DonaldKLee]

If a hacker unRSVPs, the dietary restrictions section, the safe walk check box and the RSVP button no longer appear. If a user presses the unRSVP button, a pop up message appears asking "Are you sure that you want to un-RSVP? You won’t be able to RSVP again."

[DonaldKLee]

Note: Merge dev into main after PR is approved

[github-actions[bot]]

Visit the preview URL for this PR (updated for commit 3808766):

https://nwplus-ubc--pr468-unrsvp-confirmation-ehn5p8jf.web.app

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