Add annotations/grease pencil where it's still missing

So that you are able to make notes to certain times in the animation. _No, I don't mean the frame marker stuff that already exists, I just think that being able to draw things (not influencing the actual actions) on the timeline would be pretty useful and could improve the clarity of chaotic keyframe graph chaos in more complex animations.

attached picture is an example I edited in windows snipping tool

Edit: I feel so stupid now for not thinking of this all the time: Add it everywhere. In the node editor, video editing, everywhere. (credit for this addendum goes to andreas stephens)