Add a tooltip to the issue icons with an explanation of what they actually mean

I've noticed a lock icon near the Open label of an issue:

but haven't managed to figure out what it actually means until I looked through the source code. After that, I've finally scrolled down to the form for adding a note and noticed this message:

What about adding a tooltip for the lock icon with this same message, so the meaning of the icon becomes instantly clear on hover?

The same can be done for confidential icon as well: