Add timestamp to API deployments responses

What does this MR do?

Adds the updated_at attribute to responses from the API "deployments" endpoints.

This is motivated by a specific customer request, see #33101 (closed).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content