Added initial todo functionality to collapsed sidebar

What does this MR do?

Adds todo functionality to the collapsed sidebar in the issue and mr view

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

it still needs:

• check on accessibility aria stuff
• tooltip
• loading spinner icon should temp replace the icons
• should work/show state across states of sidebar (open/closed)

Why was this MR needed?

#24805 (closed)

Screenshots (if relevant)

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 it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #24805 (closed)