Add support for String Comment Attachments

The Crowdin API has been extended with support for attachments in string comments. This enhancement allows you to attach files to string comments and manage these attachments.

The Crowdin API client libraries need to be updated to include the new endpoint and reflect the changes to existing endpoints.

**Changes:**
- [Add Comment](https://support.crowdin.com/developer/api/v2/#tag/StringAsset-Comments/operation/api.projects.comments.post) - Now supports `attachments` request parameter to attach files when creating a comment
- [Get Comment](https://support.crowdin.com/developer/api/v2/#tag/StringAsset-Comments/operation/api.projects.comments.get) - Response now includes `attachments` field with attached files

**New Endpoint:**
- [Delete Comment Attachment](https://support.crowdin.com/developer/api/v2/#tag/StringAsset-Comments/operation/api.projects.comments.attachments.delete) - Remove an attachment from a string comment

Start with the Crowdin API documentation for Add Comment, Get Comment, and Delete Comment Attachment, then locate the corresponding operations in this Go client. Update the existing comment request and response handling for attachments and add the deletion operation; done means all three API changes are represented by the client.

Written by the indexing model from the issue text.