Add error details to Distribution Release responses

The Distribution Release model returned by **Get Distribution Release** (`GET /projects/{projectId}/distributions/{hash}/release`, `api.projects.distributions.release.get`) and **Release Distribution** (`POST`, `api.projects.distributions.release.post`) now includes an optional `error` object:

- `error` — object with `message` (string); present only when the release `status` is `failed`

This applies to both file-based and string-based distribution releases, in both Crowdin and Crowdin Enterprise. Client libraries should add the field to the distribution release response models so consumers can surface release failures.

**References:**
- [Release Distribution](https://support.crowdin.com/developer/api/v2/#operation/api.projects.distributions.release.post)
- [Get Distribution Release](https://support.crowdin.com/developer/api/v2/#operation/api.projects.distributions.release.get)
- Crowdin Enterprise: [Get Distribution Release](https://support.crowdin.com/developer/enterprise/api/v2/#operation/api.projects.distributions.release.get)

Start with the response models used by `api.projects.distributions.release.get` and `api.projects.distributions.release.post`, and check how they represent file-based and string-based releases. Add the optional `error` object with its string `message` to the applicable models, then run the related tests. Done means both endpoints' response models can represent the error field when a release has failed.

Written by the indexing model from the issue text.