Add return type for CancelMerchOrder

[maxwn04]

Info

Closes #288. (If there is no issue for this pull request yet, please create one or
delete this line if the pull request is for a very minor tweak).

Description

What changes did you make? List all distinct problems that this PR addresses. Explain any relevant
motivation or context.

Adds missing return type

Changes

• Adds a api response type for cancel merch order

Type of Change

• Patch (non-breaking change/bugfix)
• Minor (non-breaking change which adds functionality)
• Major (fix or feature that would cause existing functionality to not work as
  expected)
• Documentation (A change to a README/description)
• Continuous Integration/DevOps Change (Related to deployment steps, continuous integration
  workflows, linting, etc.)
• Other: (Fill In)

If you've selected Patch, Minor, or Major as your change type, make sure to bump the version before merging in package.json!

Testing

I have tested that my changes fully resolve the linked issue ...

• locally.
• on the testing API/testing database.
• with appropriate Postman routes. Screenshots are included below.

Checklist

• I have performed a self-review of my own code.
• I have followed the style guidelines of this project.
• I have appropriately edited the API version in the package.json file.
• My changes produce no new warnings.

Screenshots

Please include a screenshot of your Postman testing passing successfully.

[github-actions]

Thanks for contributing!
If you've made changes to the API's functionality, please make sure to bump the package
version—see this guide to semantic versioning for details—and
document those changes as appropriate.

[maxwn04]

Cancel Merch Order Postman

[nik-dange]

one nit but lgtm

[nik-dange]

Also make sure to bump package.json version

[dowhep]

Great Catch with the missing return type information!

LGTM 🚀 🚀

As Nikhil noted, make sure to bump package.json version before merging