Sort secret variables by key (fix #20870)

What does this MR do?

Sort secret keys by key instead of id.

Are there points in the code the reviewer needs to double check?

Not really.

Why was this MR needed?

Since some projects may have a significant amount of variables, it may be really useful to list them by key. All similar variables in order regardless the order they've been inserted.

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 merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #20870 (closed)

May help a little while #20367 (closed) doesn`t happen.