Resolve "MR Popover is not attached in system notes"

What does this MR do?

This MR Fixes a bug where the MR popover does not show up on system notes. It makes sure the initMRPopovers is called when system notes are mounted which is happening after other discussions are mounted.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Code review guidelines
• Style guides

Performance and testing

• Tested in all supported browsers

Closes #60855 (closed)