feat: send withdrawal data unprocessed

[N-Feist]

AB#197312

All changes meet the following requirements

• Changelog entry was added
• Changes have been documented
• Changes have been tested by the author
• Changes have been tested by the reviewer
• Changes to routes were replicated in webshop package
• Plugin can be built

@plentymarkets/plentyshop

[Copilot]

Pull request overview

This PR updates the io/cancellation API endpoint to forward the incoming cancellation/withdrawal payload to CancellationRepositoryContract::submitCancellationRequest() largely unmodified (while still injecting lang), and to return the repository’s response body.

Changes:

• Stop mapping/validating individual form fields and instead forward the full request payload to submitCancellationRequest().
• Return the repository response as the API response body.
• Add structured error responses for StorefrontException and a generic \Throwable catch.

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[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 2 comments.