Ensures committing files through the UI/api does not unintentionally overwrite changes from another commit.

What does this MR do?

It implements a new validation in the File::UpdateService to check that the file being submitted for commit has not already been committed since the time the user last opened the file for editing. This prevents accidental overwriting of commits from other sources.

What are the relevant issue numbers?

Fixes #5857 (closed)

Screenshots (if relevant)

Why was this MR needed?

To prevent accidental data loss

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together