Brand store APIs: error list field name uses underscore

[Natalia Bidart]

Recently we have designed a new V2 version of our dashboard APIs, and the brand stores API were placed under this new namespace (/api/v2).

Among other changes, all the returned field names should be word-separated by dashes and not underscores. We have migrated all fields for non error responses, but we still need to migrate the error responses.

This is straightforward for errors being raised from direct brand store operations, but is not trivial for errors coming from other, shared checks, like:

* ACL checks
* User pre-requirements checks
* 404 special handler
* Generic error handlers

We need to provide a mechanism for these shared resources to be able to return the proper error list field name depending on the api version.