Added issue open icon for system note (#438202)

What does this MR do and why?

• This MR adds the system note open issue icon. See #438202 (closed)
• This MR adds the system note open merge request icon. See #438202 (comment 1729945928)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. After checking out the branch, visit any project and it's issue tab
2. Open/create an issue
3. Close the issue and reopen it
4. Try the same with Merge Requests /assign me