Annotations: Multi-row tooltip placement

**What is the problem**: To make sure tooltips don't cover annotations with the introduction of multi row. [Context](https://github.com/grafana/grafana/pull/118979#pullrequestreview-3904004027): > we should consider how the tooltip position might need to change with multilane. right now, if you pop the tooltip up for an item in the top lane, it's not really possible to quickly navigate to an annotation in the other lanes because the tooltip covers them up. I wonder if the tooltip position shouldn't be tied to the bottom of the current annotation, but instead the "lowest" annotation.