Api delete todos

What does this MR do?

It changes the DELETE /todos to only return the number of marked todos.

Why was this MR needed?

Before it returned the marked todos as an paginated array. Since we deleted/marked the todos, there was no way to get the rest of the todos.

What are the relevant issue numbers?

Closes #19678 (closed)

Does this MR meet the acceptance criteria?

- [x] 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