fix: cancelledby to work on api v1

[Shpadoinkle]

What does this PR do?

assigns cancelledby to the body, so it can actually be read and used by the handler.

api v1 support was a requirement of the original feature request.

Mandatory Tasks (DO NOT REMOVE)

• I have self-reviewed the code (A decent size PR without self-review might be rejected).
• I have updated the developer docs in /docs if this PR makes changes that would require a documentation change. If N/A, write N/A here and check the checkbox.
• I confirm automated tests are in place that prove my fix is effective or that my feature works.

How should this be tested?

• passing in a cancelledBy value on the query param should no longer be ignored. and actually store the value to the databse.

[vercel]

@Shpadoinkle is attempting to deploy a commit to the cal-staging Team on Vercel.

A member of the Team first needs to authorize it.

[graphite-app]

Graphite Automations

"Add consumer team as reviewer" took an action on this PR • (02/12/25)

1 reviewer was added to this PR based on Keith Williams's automation.

"Add community label" took an action on this PR • (02/12/25)

1 label was added to this PR based on Keith Williams's automation.