Change task list item system note from task to checklist item

What does this MR do and why?

In #368028 (closed) we are renaming task => checklist item. This MR creates all new system notes with the new name and also renders the new name for older system notes.

We have two follow up issues to finish the transition:

• Fix existing system notes for Issue task updates (#369930 - closed)
• Remove `note` and `note_html` method from `Note... (#369923 - closed)

How to set up and validate locally

1. Create a list in an issue's description such as:
   • one
   • two
2. Checking or unchecking should create system notes on the issue.
3. Before the message would read marked the task **Task 1** as incomplete, now it should read marked the checklist item **Task 1** as incomplete in new and old system notes

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #368028 (closed)