feat(server): add comment-attachment storage (#12911)

close CLOUD-230












#### PR Dependency Tree


* **PR #12911** 👈
  * **PR #12761**
    * **PR #12924**
      * **PR #12925**

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added support for uploading and retrieving comment attachments in
workspace documents via a new API endpoint.
* Introduced a service for managing comment attachments, including
storage, retrieval, deletion, and URL generation.
* Implemented localized error messages and improved error handling for
missing comment attachments.

* **Bug Fixes**
  * Improved error feedback when comment attachments are not found.

* **Tests**
* Added comprehensive tests for comment attachment storage, retrieval,
deletion, API endpoint behavior, and permission checks.

* **Documentation**
* Updated GraphQL schema and localization files to include new error
types for comment attachments.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/schema.gql

@@ -540,6 +540,7 @@ enum ErrorNames {
   CAN_NOT_BATCH_GRANT_DOC_OWNER_PERMISSIONS
   CAN_NOT_REVOKE_YOURSELF
   CAPTCHA_VERIFICATION_FAILED
+  COMMENT_ATTACHMENT_NOT_FOUND
   COMMENT_NOT_FOUND
   COPILOT_ACTION_TAKEN
   COPILOT_CONTEXT_FILE_NOT_SUPPORTED