Cancel workshop feature

[KimberleyCook]

Description of the issue 📄

There are occasions when workshops need to be cancelled. There needs to be a checkbox on the admin page of the workshops that does this. When checked

• RSVP should be closed
• A banner should appear on the workshop page
• All attendees should be emailed
• Workshop reminder email should not be sent

Screenshots 📷

Steps to fix 🛠

To do 📋

• [ ] Claim this issue (comment below, or assign yourself if you are part of the codebar org)
• [ ] Fork and clone the repository
• [ ] Update the relevant files. Follow the steps to fix section in this issue.
• [ ] Commit your changes as one commit. Use the title of this issue as your commit message
• [ ] Submit a pull request
• [ ] Mention this issue in the PR description by including it's number
• [ ] Have your pull request reviewed & merged by a codebar team member