Commits API: Preserve file content in move operations if unspecified

What does this MR do?

Restores the previous behaviour of the commits API, where moving (renaming) a file without specifying the content would preserve the file's content across the move operation.

What are the relevant issue numbers?

Closes #51083 (closed)

Closes #52974 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• [-] Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.