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 by locating the distribution release response models and the definitions for api.projects.distributions.release.get and api.projects.distributions.release.post. Compare the documented response shape, then verify that both file-based and string-based releases expose the optional error.message field when status is failed, for Crowdin and Crowdin Enterprise variants.

索引モデルが issue の本文から書いたものです。