bug: incorrect openapi.yml for DuplicateOrder

[mfw78]

Problem

When attempting to add an order to the API more than once, the API returns DuplicatedOrder, despite the openapi.yml indicating it should be DuplicateOrder.

Impact

With a recent push to reduce API resource consumption, this may result in excessive programmatic retries of the API, leading to excessive resource consumption.

To reproduce

1. Use https://api.cow.fi/docs/#/
2. Attempt to post the same order twice.
3. Observe the second attempt showing DuplicateOrder.

Expected behaviour

The API gives the correct response according to the openapi.yml.

services version/commit hash and environment

Version: v2.226.00
Environment: production (mainnet)

Additional context

This error was found during the course of testing the watch tower.