13495-a: Create DesignAtVersion model

What does this MR do?

This adds data models that represent designs at a given version. This is required for !15260 (merged) in order to meet the front-end need for reliable meaningful identifiers.

This MR contains the backend model changes only.

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

Performance and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

See #13495 (closed)