feat: delete classroom button on classroom cards

[d282liu]

Notion ticket link

Delete classroom button

Implementation description

• created delete class mutation
• call mutation from front end when clicking delete button in drop down

Steps to test

1. Try deleting classes

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[github-actions]

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[joyce-shi]

very nice (:

upon double-checking

[carissa-tang]

nice! lgtm