Show tooltip when hovering over "Offline update"

Most of the other indicators related to Entity conflicts have helpful tooltips. The "Offline update" badge does not. I think it would be helpful to have something like

> This version was created as part of a chain of updates made while offline.

I could see the argument that this doesn't add a ton but I think it unpacks the concept a bit. Maybe we can come up with better wording.

Note: https://github.com/getodk/central-frontend/pull/1100 hides the offline update details for standard use.