feat: add endpoint for cancelling orders

[pavelbrm]

Summary

This PR adds a new endpoint which works similar to the existing one for cancelling orders expect for it does not handle subscription cancellations in Stripe. Instead, it just updates the order status to canceled.

I've considered going with PUT and/or using 204 response, but rejected those options because they did not fit this use case. So had to stick with DELETE and 200 in response, with an empty body.

Also, for some tests .ErrorIs and .Nil for errors were not applicable, details for which I could provide if needed. Had to use the simple .Equal because it simply works, and does the comparison the way I need it.

Hopefully the points above provide the necessary context during review.

Type of Change

• Product feature
• Bug fix
• Performance improvement
• Refactor
• Other

Tested Environments

• Development
• Staging
• Production

Before Requesting Review

• Does your code build cleanly without any errors or warnings?
• Have you used auto closing keywords?
• Have you added tests for new functionality?
• Have validated query efficiency for new database queries?
• Have documented new functionality in README or in comments?
• Have you squashed all intermediate commits?
• Is there a clear title that explains what the PR does?
• Have you used intuitive function, variable and other naming?
• Have you requested security and/or privacy review if needed
• Have you performed a self review of this PR?

Manual Test Plan

[clD11]

Approved with comments and questions.